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ColoradoProspector
Hey Everyone, thought this was an interesting tid bit worth posting........Colorado produced North Americas largest faceted diamond. Here is a bit of info from the Kelsey Lake mine.........
QUOTE
The Kelsey Lake mine, located almost on the Colorado-Wyoming line, includes some eight kimberlite pipes, the two largest of which have a combined area of about 20 acres (Hausel 1998). The mine was first opened by Redaurum, a Canadian company; ownership changed to McKenzie Bay International, and it is currently owned jointly by Roberts Construction and BJ&J Jewelers, two North Dakota companies. It was operated from 1996 to 1998 and produced North America's largest-known cut diamond--a pale yellow 16.86-carat faceted stone that was cut from a well-formed 28.18-carat crystal found in 1997. Another, a 28.3-carat yellow diamond mined in 1996, was cut into a 5.39-carat pear-shaped stone.


I'm still looking for some pics of the faceted stones.

CP
J.D. Dana
Some more kimberlite info:

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State Line Diamond-Bearing Kimberlite District

Diamond-bearing kimberlite pipes were discovered in northern Colorado and southern Wyoming in the 1970s, and the flurry of exploration that located some thirty-five pipes (depending on how one counts the individual pipes and dikes, which tend to occur in clusters) led to full-scale open-pit diamond mining at the Kelsey Lake mine from 1996 to 1998. The mine, located almost on the Colorado-Wyoming state line south of Tie Siding, Wyoming, produced numerous gem-quality diamonds, including two that, coincidentally, weighed 28.2 and 28.3 carats. The mine has been inactive since 1998, but the corporate owners continue to express hope of reopening it after improvements to crushing and recovery equipment. The minerals and the geology and history of the discovery of the diamond pipes are described in detail in numerous publications (Collins 1982; Collins and Heyl 1984; Coopersmith and Schulze 1996; Eckel 1997; Cappa 1998; Hausel 1998; Hausel and Sutherland 2000; Murphy 2000).

The likelihood of a collector actually finding a diamond either in kimberlite rock matrix or in soil or alluvium weathered from the pipes is small; the typical diamond content of the State Line pipes is less than 0.1 carat per ton. However, kimberlite "indicator minerals" that accompany the diamonds are distinctive and can readily be found in the rock or as loose mineral grains. These minerals include pyrope (garnet), typically dark red to purplish-red; emerald-green "chrome diopside" (chromium-rich diopside); and black, submetallic magnesian ilmenite (a magnesium-rich variety of ilmenite, characteristic of deep origin in the earth's mantle). Other associated minerals include olivine (commonly altered to serpentine), phlogopite, enstatite (hypersthene), and many other trace accessory minerals. Some of the mantle-derived minerals that occur as rounded, anhedral to subhedral crystals called megacrysts or xenocrysts can be quite large; pyrope crystal fragments weighing more than 2 pounds and chrome diopside and enstatite crystals more than 8 cm across have been reported (Eckel 1997).

Although most of the kimberlite pipes are on private property and are thus off-limits, a few can be visited by collectors. The Chicken Park group of pipes is located on Roosevelt National Forest land north of Prairie Divide and is easily reached by a decent dirt road that passes just to its north. The largest diatreme outcrops in a meadow partly surrounded by trees--typical of kimberlites, which tend to be less forested than surrounding areas--and one can readily find samples of the kimberlite rock and its constituent minerals. Another accessible pipe is the Green Mountain kimberlite, located on forested Boulder City Park land that is east of Green Mountain (one of many Green Mountains in Colorado), south of Flagstaff Mountain, and west of Saddle Rock, in the SW 1/4 of sec. 1, T. 1 S., R. 71 W. It can be reached by starting on the Greenman hiking trail and then cutting due north, going down into a steep valley and up the opposite hillside. The pipe is well exposed as a small knoll about 140 feet in diameter, and it is easy to find fresh samples of the kimberlite and its minerals. This, the southernmost of all the known kimberlite pipes in this region, is the one pipe from which no diamonds at all have been reported, perhaps because it has not been sampled in bulk due to its location on park property, or because the diamonds are in fact not present.
J.D. Dana
Here some more info from the same article on CO collecting locals. Note: I probably should have found a better spot for this so feel free to move this post:

QUOTE
Colorado mineral collecting localities.(Cover Story)
From: Rocks & Minerals  |  Date: 9/1/2005  |  Author: Modreski, Peter J.
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Colorado is, of course, famous for its many minerals and mineral deposits, ranging from the gold and silver that first brought prospectors and other adventurous pioneers to the state, to the other ore and gangue minerals of hydrothermal veins, of pegmatites, of regionally and contact metamorphosed rocks, of volcanic and other igneous rocks, and minerals of veins, concretions, nodules, and silicified fossils in sedimentary rocks. This article surveys some of the state's best-known mineral localities, with an emphasis on those that are, or have been in the recent past, readily able to be visited and collected. It is important to preface the article with a reminder that any collecting trips should only be made to locations that are known to be on public land with no prohibitions on collecting or to private land or mining claims for which permission has been obtained.

Collecting Guides

Several books have been written as guides to mineral collecting in Colorado. A classic, which went through three major editions between 1958 and 1972 (plus an earlier, 1951 version with a slightly different title), is Colorado Gem Trails and Mineral Guide, by Pearl (1951, 1958, 1965, 1972). Though some of its directions are now out of date and many localities are no longer accessible, the book is still in print and is still a useful guide to collecting. Currently, the most comprehensive and up-to-date guidebook to the state's minerals is Colorado Rockhounding, by Voynick (1994). Other published collecting guides include those by Kapelle (1995) and Mitchell (1992) as well as several smaller booklets (Baldwin 1979; McKinney and McKinney 1987). A review article on Colorado gemstone localities (Murphy and Modreski 2002) also describes in greater detail many of the localities discussed here, plus some others.

Another classic book that is still useful in its original edition is Minerals of Colorado--A 100-Year Record, by Eckel (1961). Copies are still often available, and a facsimile reprint edition was published commercially in the 1990s. However, the book was totally revised and republished as an enlarged, hardbound volume with color plates by a group of authors from the Colorado Chapter of the Friends of Mineralogy, the Denver Museum of Natural History, and the U.S. Geological Survey (Eckel 1997). The seven authors include Eckel, who was deceased by the time the book was published.

Though not specifically mineral collecting guides, several excellent guides to the geology of Colorado should be mentioned: the popular Roadside Geology of Colorado, now in its second, revised edition (Chronic and Williams 2002); the well-written and strikingly illustrated Messages in Stone, published by the Colorado Geological Survey (Matthews, Keller-Lynn, and Fox 2003) as a replacement and modernization of the long-popular and now out-of-print Prairie Peak and Plateau (Chronic and Chronic 1972); as well as Guide to the Geology of Colorado (Taylor 1999) and Geology of Colorado Illustrated (Foutz 1994).

Collecting Localities

Pikes Peak Batholith

A rich source of pegmatite minerals, the Pikes Peak batholith extends over 1,000 square miles and includes numerous localities for smoky quartz, the amazonite variety of microcline, topaz, goethite, fluorite, zinnwaldite, and a host of less common minerals. Numerous books and articles have been written about the region and its minerals, and the reader is referred to them for detailed descriptions of all the minerals and their localities. Good sources of information include the general articles on the minerals of the batholith by Muntyan and Muntyan (1985) and Raines (2001); on amazonite by Odiorne (1978) and Foord and Martin (1979); topaz (Modreski and Michalski 1996; Mexander 1996; Thompson 2001); "onegite" (amethystine smoky quartz with goethite inclusions; Berry 2001); and micas of the batholith (Foord 1995; Kile and Foord 1998). In addition, several volumes of papers and field guides from mineralogical symposia have been published about the Pikes Peak batholith (Modreski 1986; Simmons, Webber, and Falster 1999), and a wealth of information about all the specific pegmatite minerals and their reported localities is contained in the revised Minerals of Colorado (Eckel 1997).

Mineral localities within the batholith, all discussed in many of the above-cited publications, include (listing them in a generally clockwise direction) Glen Cove, Crystal Park, Cameron Cone, Hunters Run, Sentinel Rock, Specimen Rock, Cheyenne Canyon, Stove Mountain, St. Peters Dome, Mount Rosa, Crystal Peak, the Tarryall Mountains, Harris Park, Wigwam Creek, and the Devils Head area. Most of the crystal-producing localities contain what are termed miarolitic cavity pegmatites, dikes that may appear as thin dikes or even just iron-coated fracture surfaces in the granite but that locally bulge or expand into crystal-lined pockets to several feet high and tens of feet across.

A distinct portion of the batholith on the southeast side of Pikes Peak, including the area around Stove Mountain, St. Peters Dome, and Mount Rosa, is particularly rich in fluorine and alkali metals and hosts a number of unusual minerals, including astrophyllite, riebeckite, bastnasite, genthelvite, zircon, and rare fluoride minerals, including cryolite, elpasolite, ralstonite, thomsenolite, and others.

The Crystal Peak area, located north of the towns of Florissant and Lake George, lies within or adjacent to a concentric series of late intrusions into the main Pikes Peak batholith that is known as the Lake George ring complex. The igneous rocks in it include a variety of types, ranging from fine-, medium-, and coarse-grained granite, to syenite, monzonite, diorite, and gabbro, and they encompass many pegmatite mining claims and mineral localities. A recent spectacular find, which included two smoky quartz crystals about 4 feet in length and several cubic fluorite crystals to about 10 cm across, was made in 2002 on a claim along Crystal Creek, north of Florissant and Lake George (Berry and Fretterd 2003). Although most of the best and longest-known pegmatite localities here are held as private mining claims, and the southern part of the area including Crystal Peak itself is privately owned and subdivided into homesite lots, there is still abundant opportunity for new prospecting to find more undiscovered pegmatite occurrences in the unclaimed land within the Pike National Forest.

The Tarryall Mountains form the western edge of the Pikes Peak batholith. Their southern part is composed of a separate granite pluton, the Redskin Stock. The area is noted for its topaz-bearing crystal pockets (Modreski and Michalski 1996). The Spruce Grove Campground is a common starting place for hiking trips into the southern Tarryalls to hunt for topaz, which has been found at many sites in and near the valley of Beaver Dam Creek, both in bedrock and as loose, transported crystals in gravelly alluvium. Through last year, a commercial gem topaz-mining operation was conducted by Walter Rubeck as the Topaz Mountain Gem Mine. It was located at the southern end of the Tarryall Mountains. Alluvial gravels containing scattered topaz crystals were excavated and sold to collectors by the bucket. Rubeck died in January 2005, and the claims are now owned by mineral dealer Joe Dorris, of Colorado Springs.

A distinct type of pegmatite occurrence within the Pikes Peak batholith occurs in the South Platte pegmatite district. Rather than consisting of small dikes and crystal-bearing open pockets within the granite, it consists of large, vertical, cylindrical and concentrically zoned pegmatite bodies that cut through the surrounding granite. There are about fifty such pegmatites, generally concentrated in the northern part of the Pikes Peak batholith; they are described in detail by Simmons and Heinrich (1980). Most of the larger pegmatites were mined from the 1920s into the 1960s for potash feldspar as well as for decorative white quartz, fluorite, and rare-earth minerals. Although these massive pegmatites generally lack any open cavities that would have permitted good crystal development, some of them have yielded good fluorite crystals as well as generally more massive specimens of quartz, microcline, biotite, and an abundance of rare-earth, uranium, and thorium-bearing minerals, including gadolinite, samarskite, monazite, allanite, xenotime, thorite, and others. The district was formerly accessible via a Pike National Forest road, passing through the Top of the World Campground; however, the Buffalo Creek forest fire of 1996 destroyed the campground, and the roads are closed to public use. The only access now is by hiking trails, including the Colorado Trail that skirts the northern edge of the district.

Mount Antero and Mount White

These adjacent peaks in the Sawatch Range, Mount Antero (a "fourteener" at 14,269 feet) and Mount White (13,600 feet) are famous for their occurrences of aquamarine (the blue, gemmy variety of beryl) as well as other pegmatite and related minerals, including smoky quartz, albite, fluorite, topaz, and the beryllium minerals phenakite and bertrandite. Antero Aquamarines (Jacobson 1993) gives an excellent description of the history and mineralogy of the area. Other sources include earlier articles by Jacobson (1979, 1984) as well as the recent description by Lees (2005) of spectacular large aquamarine crystals on matrix with smoky quartz found in summer 2004. Aquamarine is, of course, the state gemstone of Colorado, adopted in 1971. As time goes by, it gets more difficult to find new crystal pockets, the four-wheel-drive road to the top gets rougher, and more areas tend to have claims filed and are marked "off limits"; nevertheless, collectors keep digging and prospecting here, and first-class crystals and pockets continue to be found.

Ruby Mountain

Ruby Mountain, a mass of rhyolite lava located on the east bank of the Arkansas River near Nathrop, Chaffee County, has been a popular collecting area for many decades. The 'rubies" found her are red spessartine garnets, to about 1.5 cm in diameter, that occur in gas cavities (lithophysae) in the rhyolite. Present along with the spessartine are colorless to amber-colored topaz crystals, typically quite small but occasionally as large as 2 cm (Modreski and Michalski 1996). Formerly, most of the mountain, though privately owned, could be accessed by paying a small fee; but in recent years, following the sale of the property and construction of several homes, the talus hillside on the west side--the best source of specimen collecting--has not been accessible. A trail up the east side of the mountain, on public land, can still be taken, but collecting is now much more difficult in the limited amount of solid, unbroken rhyolite exposed on the summit. A popular curiosity that can still be collected are "Apache tears," small rounded nodules of obsidian that weather out of perlite (hydrated obsidian) at a small former quarry site on the east side.

Calumet Iron Mine

The Calumet mine, near Salida in Chaffee County, a locality frequently visited by Colorado collectors, consists of open cuts on a steep hillside and underground workings that are somewhat dangerous and probably no longer accessible. It has been a favorite locality for epidote, quartz, magnetite, diopside, "uralite" (actinolite pseudomorphs after diopside), grossular, and associated minerals. The magnetite, uralite, and other minerals can be exposed by etching away the enclosing calcite with hydrochloric acid. The nature of the deposit is contact metamorphic, in which calcareous and silty sedimentary rocks have been baked and altered by a sill of the Whitehorn Granodiorite. An inactive white marble quarry is located about a half-mile north of the mine. Also on a hillside to the north is a contact metamorphosed bed rich in small, dark blue, platy corundum crystals. Probably the most distinctive mineral from the deposit is epidote, as equant, diamond-shaped, dark green individual crystals typically about 1-1.5 cm to as much as 5 cm in size; some are associated with clear quartz crystals to 6 cm (Minch 1983; Eckel 1997).

South Park Peridot Locality

An area that has come into prominence in the past decade is composed of one or more mesas that form part of the hills near the southern edge of South Park. Here, olivine (peridot when gemmy) grains or anhedral crystals weather out of basaltic lava. Murphy and Modreski (2002) described the area briefly; it is in sec. 35, T. 15 S., R. 76 W., south of Herring Park and west of Badger Creek (much of the locality is on public land, but some portions may be on restricted state land, private property, or under active mining claims). Most of the olivine grains are small, but dazzling bright green peridot gemstones approaching 3 carats have been faceted from the larger pieces, notably by gemologist John Rhoads of Salida, Colorado.

Hartsel Barite Locality

Another well-known locality for distinctive barite crystals is in prospect pits where barite has been excavated from red beds of the Pennsylvania-Permian Maroon Formation in South Park, just south of the town of Hartsel, Park County. The barite occurs as sheaves and clusters of tabular crystals, ranging from pale yellow to pale blue; exposure to sunlight is reliably reported to deepen the blue color. The barite site is under an active mining claim, but permission to visit the diggings can often be obtained.

Del Norte Thunder-Egg Locality

A well-known locality for agate or chalcedony nodules in rhyolite (thunder eggs) is near the Twin Mountains, northwest of Del Norte in Saguache County. Kile (2002) gave a detailed description of the area and the nodules, the best of which are famous for the golden-yellow to red, moss and plume agate they contain.

Grand Junction (Book Cliffs)

Septarian concretions, some as much as 6 feet in diameter, occur in the Mancos Shale north of the town of Grand Junction where the land slopes upward toward the base of the Book Cliffs. Most contain massive or crystalline calcite that lines the hollow portions of the concretions; some also contain fine, water-clear barite crystals as long as 15 cm (Eckel 1997; Muntyan 1998; Murphy and Modreski 2002). Similar concretions with calcite and barite crystals occur in the Carlile Shale of Cretaceous age in Las Animas, Pueblo, Otero, and Huerfano counties of southeast Colorado.

Fremont County Pegmatite District

Also traditionally known as the Eight Mile Park district, this area includes several large pegmatites in the area from the Royal Gorge north across U.S. Highway 50 toward Park County and the town of Guffey. Many of these pegmatites were quarried before and after World War II for feldspar, beryl, mica, columbite-tantalite, and other minerals. Some of the pegmatites contain only coarse-grained microcline feldspar, quartz, muscovite, and black tourmaline (schorl). Most of the larger quarries are on private land, and some are still operated occasionally. Of the better-known quarries, the Mica Lode and the Meyers quarries, both on private property, are located just east of the road leading to the Royal Gorge. Large beryl crystals and very coarse mica books were abundant at the Mica Lode, and the Meyers quarry contained lithium minerals including pink elbaite, pale-colored lepidolite, and crude crystals of the amblygonite-family mineral natromontebrasite. The district is bordered on the north by the Micanite-Guffey district and on the west by the Texas Creek area. Here, the Devils Hole mine is noted for beryl, rose quartz, columbite-tantalite, and many other minerals, and the Chief Lithium pegmatite contains green schorl-elbaite tourmaline and lepidolite. Eckel (1997) gives details and more published references about all of these pegmatites and their minerals. Access to these quarries, most of which are located on private land, has varied over the years.

Grape Creek area, Fremont County

Grape Creek, a tributary of the Arkansas River west and south of Canon City, cuts through rugged country of Precambrian granite and metamorphic rocks. A group of localities on the east side of Grape Creek, in SE 1/4 sec. 16, T. 19 S., R. 71 W., contains gahnite, cordierite, and dumortierite. Large, dark green gahnite crystals more than 5 cm on edge have been collected from a quartz lens in schist. The grayish-blue, partly gemmy cordierite, when first discovered in the early twentieth century, was mistakenly reported as corundum. Not until the site was revisited by local collectors in 1987 was the material correctly identified as cordierite (Jacobson 1988). The best descriptions of the area are in Jacobson (1988) and Eckel (1997).

State Line Diamond-Bearing Kimberlite District

Diamond-bearing kimberlite pipes were discovered in northern Colorado and southern Wyoming in the 1970s, and the flurry of exploration that located some thirty-five pipes (depending on how one counts the individual pipes and dikes, which tend to occur in clusters) led to full-scale open-pit diamond mining at the Kelsey Lake mine from 1996 to 1998. The mine, located almost on the Colorado-Wyoming state line south of Tie Siding, Wyoming, produced numerous gem-quality diamonds, including two that, coincidentally, weighed 28.2 and 28.3 carats. The mine has been inactive since 1998, but the corporate owners continue to express hope of reopening it after improvements to crushing and recovery equipment. The minerals and the geology and history of the discovery of the diamond pipes are described in detail in numerous publications (Collins 1982; Collins and Heyl 1984; Coopersmith and Schulze 1996; Eckel 1997; Cappa 1998; Hausel 1998; Hausel and Sutherland 2000; Murphy 2000).

The likelihood of a collector actually finding a diamond either in kimberlite rock matrix or in soil or alluvium weathered from the pipes is small; the typical diamond content of the State Line pipes is less than 0.1 carat per ton. However, kimberlite "indicator minerals" that accompany the diamonds are distinctive and can readily be found in the rock or as loose mineral grains. These minerals include pyrope (garnet), typically dark red to purplish-red; emerald-green "chrome diopside" (chromium-rich diopside); and black, submetallic magnesian ilmenite (a magnesium-rich variety of ilmenite, characteristic of deep origin in the earth's mantle). Other associated minerals include olivine (commonly altered to serpentine), phlogopite, enstatite (hypersthene), and many other trace accessory minerals. Some of the mantle-derived minerals that occur as rounded, anhedral to subhedral crystals called megacrysts or xenocrysts can be quite large; pyrope crystal fragments weighing more than 2 pounds and chrome diopside and enstatite crystals more than 8 cm across have been reported (Eckel 1997).

Although most of the kimberlite pipes are on private property and are thus off-limits, a few can be visited by collectors. The Chicken Park group of pipes is located on Roosevelt National Forest land north of Prairie Divide and is easily reached by a decent dirt road that passes just to its north. The largest diatreme outcrops in a meadow partly surrounded by trees--typical of kimberlites, which tend to be less forested than surrounding areas--and one can readily find samples of the kimberlite rock and its constituent minerals. Another accessible pipe is the Green Mountain kimberlite, located on forested Boulder City Park land that is east of Green Mountain (one of many Green Mountains in Colorado), south of Flagstaff Mountain, and west of Saddle Rock, in the SW 1/4 of sec. 1, T. 1 S., R. 71 W. It can be reached by starting on the Greenman hiking trail and then cutting due north, going down into a steep valley and up the opposite hillside. The pipe is well exposed as a small knoll about 140 feet in diameter, and it is easy to find fresh samples of the kimberlite and its minerals. This, the southernmost of all the known kimberlite pipes in this region, is the one pipe from which no diamonds at all have been reported, perhaps because it has not been sampled in bulk due to its location on park property, or because the diamonds are in fact not present.

Crystal Mountain Pegmatite District

This district, about 6 square miles in area, consists of large pegmatites enclosed within schists and other metamorphic rocks and granites. It is in Larimer County, centered near Crystal Mountain and lying north of Big Thompson Canyon and south of Cache la Poudre Canyon. Access to much of the area is via the Buckhorn Canyon Road. Jacobson (1986a) lists seventeen major pegmatites, most of which have been mined for beryl, feldspar, tantalite, or other minerals, plus a long list of the minerals found in the district, including beryl, alluadite, amblygonite, bismutite, chrysoberyl, lepidolite, purpurite, tantalite, schorl, and many more. (See also Jacobson 1985, 1986a,b.)

Genessee "Dike" Calc-Silicate Road Cut

This once-popular roadside locality just west of the Golden and Denver metropolitan area has been extensively collected for many years, and good specimens are now fairly difficult to find. It was described by Kile and Modreski (1990); notable minerals have included grossular, hedenbergite, anatase, epidote, titanite, and scheelite. However, all one usually finds now are hollow molds of massive quartz that once surrounded large euhedral garnet crystals.

North Table Mountain, Golden

North and South Table Mountains, which lie on either side of Clear Creek just east of downtown Golden, are a classic locality for zeolite minerals. The zeolites occur in gas cavities (vesicles) in lava flows that cap the mesas. Two thick lava flows form the cap, with a third, thinner and discontinuously exposed flow below. Recent geologic mapping by retired U.S. Geological Survey geologist Harald Drewes has proposed the presence of a fourth lava flow, forming one tongue of lava filling a former valley on the north side of North Table Mountain, immediately beneath the lower capping flow. Zeolite minerals are most abundant in the lower capping flow, and more have been collected on North Table Mountain than on South Table Mountain. The lavas are shoshonite, a dark gray lava that resembles basalt but is technically classed as a potassium-rich basaltic trachyandesite. The geology and zeolite mineralogy of the lava flows was described by Kile and Modreski (1988a) and updated by Kile (2004); Bartos (2004) also gave an interesting account of some of the early collecting history of the Table Mountains. The most common zeolite minerals found in the Table Mountain lavas are thomsonite, analcime, and chabazite, but ten other zeolites have been reported, plus a few nonzeolite minerals, including calcite, chrysocolla, fluorapophyllite, and the clay mineral nontronite.

Recently, Jefferson County Open Space, fulfilling a longtime goal, acquired essentially all of the summit area of North Table Mountain. Although the normal policy of the county is to prohibit any removal of natural materials from any of its Open Space parks, ongoing discussions with collectors and others are developing a policy that will permit mineral collecting at least at one, possibly more, sites on the mountain, particularly at the old paving-stone quarry located on the south rim of the mountain, just above the large, multiply benched road cut above Colorado Highway 58. Open Space trails and trailheads are still in the process of being developed, but several convenient access points exist on all sides of the mountain, including the following:

(1) On the west side is a paved trailhead parking area off Wyoming Circle near the intersection of Ford Street and Pine Ridge Road, just east of State Highway 93. A crude trail connects to an old gravel road that climbs to the top of the mountain.

(2) On the south side is a parking lot and trailhead maintained for rock-climbing access on the southwest side of North Table Mountain, located at the end of Peery Parkway, above the Boyd Street exit from Colorado Highway 58.

(3) On the southeast side a crude trail begins near the entrance ramp from Easley Road to westbound Colorado Highway 58. The trail, which ascends along the east edge of the large multibenched road cut in the beds of the sedimentary Denver Formation that underlies the lava flow, provides access to a small old quarry in the cliff face where paving stones were trimmed out of solid, dense lava that is free of fractures and zeolites. However, an abundance of lava boulders rich in zeolite-containing cavities (material that fell down from the cliffs and was probably not used for paving stones) is present in the quarry.

(4) On the east side a trail, with Open-Space trailhead access now under construction, off Ulysses Way west of Easley Road, leads up a large valley incised into the southeast part of the mountain.

(5) Further north on the east side, parking in Tony Grampsas Park at the end of Salvia Street north of West 44th Avenue connects to a trail that crosses Easley Road and climbs to the head of a smaller valley on the northeast part of the mountain.

(6) On the north side, south of West 58th Avenue, a road connects to a trail that follows a jeep road to the top of the mesa.

A number of other localities on the mountain have produced abundant zeolite minerals, mostly from the lower capping lava flow on the east side of the mountain. Collectors should be sure to check with Jefferson County Open Space before attempting to collect at any sites other than the paving-stone quarry, especially if a group field trip is planned.

Stoneham, Weld County

The area near Stoneham in Colorado's northeastern plains is a classic collecting area for attractive, blue barite crystals. The crystals occur in clay beds of the Chadron Formation of Oligocene age, part of the White River Group of sediments, famous for its Tertiary mammal fossils. The area and the barite were described by Bennett (1986) and by Modreski, Lees, and Wilson (1990). The latter article described the excavations that Bryan Lees organized in 1989 with mechanized digging equipment, resulting in the recovery of many superb specimens and clusters of barite, with crystals to 10 cm long. Although some barite is found in isolated pockets in the clay, the best and most abundant crystals occurred along a fault zone cutting the clay bed, in open or clay-filled cavities to 12 feet long, 4 feet wide, and 8 inches high. Drusy yellow calcite was associated with some of the barite. The site has been a popular collecting place for groups from Colorado mineral clubs through the decades. Because much of the best collecting area is on state-owned land leased to local ranchers, consulting with local mineral clubs or participating in their trips is the best way to obtain permission to visit the area.

Other Localities

This article only scratches the surface of the many Colorado mineral localities, and I have not tried to even touch on all the mineralized districts. Innumerable old mines exist throughout the San Juan Mountains and elsewhere in the Colorado mineral belt; many are closed, posted, or otherwise inaccessible, but others can still be reached for collecting. Many of these localities are described in the articles by Muntyan (1988a,b, 1994, 1995, 1996, 1998, 1999, 2000), Kile, Modreski, and Kile (1991), and Raines (1992, 1997a,b, 2000a,b). The major mines of the San Juans, such as the Camp Bird, Idarado, and Sunnyside mines, as well as almost all of the mines of any size in Colorado, are all now closed and inaccessible; however, at some it is still possible to collect specimens on parts of the outlying dumps, and mineral clubs often receive permission to visit mine properties that are otherwise closed. For example, recently it has been possible to collect specimens (at a $2-per-pound fee) on the dumps of the Last Chance mine in Creede, through the caretaker of the property.

Several other "visitable" localities are worth mentioning. The zeolite occurrences near Treasure Falls west of Wolf Creek Pass (Hampson 2004) are still a source of specimens. At several localities near Leadville, including along Highway 91 south of Fremont Pass and on Prospect Mountain north of the Mosquito Pass Road, orthoclase crystals weather out of porphyry sills, along with bipyramidal quartz crystals (high temperature, or beta-quartz) (see Eckel 1997). Many metamorphosed, massive sulfide ore deposits of Precambrian age occur throughout central Colorado in Gunnison, Chaffee, Park, Fremont, and Custer counties. They contain sulfide minerals as well as metamorphic minerals that include cordierite, gahnite, epidote, garnet, amphiboles, schorl, and many others (see Heinrich 1981; Eckel 1997). Metamorphosed calc-silicate deposits of similar age and origin occur in the same region and lack sulfide minerals but contain grossular, vesuvianite, epidote, pink zoisite (variety thulite), scheelite, diopside, and related minerals (Heinrich 1981). Amethyst occurs at several localities in Colorado (Michalski 1984; Murphy and Modreski 2002), though it has become much more difficult to arrange access to the most popular amethyst locality, the Rainbow Lode claim near Red Feather Lakes, to which clubs, at one time, could schedule frequent collecting trips. It is also much more difficult to find any of the sparse remaining amethyst crystals. Mineral clubs often have success in arranging weekend field trips to visit even active quarries, such as the limestone quarries near Portland (Fremont County) and near Lyons and Fort Collins (Boulder and Larimer counties). Considerable petrified wood is found near the towns of Parker, Kiowa, Elizabeth, and Elbert, in Douglas and Elbert counties, though most of it is on private land and requires cultivation of congenial relations with property owners. There are many more localities and districts that could be mentioned; this is but a sampling.

To recap advice about how to learn exactly where to find current, good collecting sites in the state: read and examine the various published books, articles, and maps about areas of interest; talk to people at local rock shops; consider joining one of the many Colorado gem and mineral clubs * to get firsthand advice and to visit "special" sites for which the groups periodically obtain permission; and, armed with books, maps, and advice, try seeking out new and productive localities on your own!

[FIGURES 36-41 OMITTED]

Colorado Minerals on Display: Museums Worth Visiting

Colorado School of Mines (CSM) Geology Museum, 13th and Maple Streets, Golden, CO 80401. Telephone 303/273-3815; http://www.mines.edu/academic/geology/museum/. 9 A.M.-4 P.M. Mon.-Sat., 1-4 Sun. (closed Sundays during the summer). This superb modern museum was completed and opened in 2003. Displays feature Colorado rhodochrosite, silver, amazonite, and other local minerals, as well as educational displays of mineral properties, birthstones, state minerals and rocks, radioactive minerals, and more. The CSM Museum is the best place to see displays of minerals from Jefferson County, Colorado, including zeolites from the Table Mountains.

Denver Museum of Nature and Science, 2001 Colorado Blvd., Denver, CO 80205. Telephone 303/3227009; http://www.dmns.org/main/en/. The Coors Mineral Hall contains excellent displays of Colorado and worldwide minerals. Highlights include the Alma King, the largest crystal of rhodochrosite recovered from the Sweet Home mine; a 6-foot reconstructed wall of rhodochrosite crystals from the Sweet Home mine; a spectacular display of Breckenridge gold specimens, including Tom's Baby, an 8-pound mass of Breckenridge gold; the 117-(troy) pound Summitville Gold Boulder; and a case of Colorado gemstones.

National Mining Hall of Fame and Museum, 120 W. 9th St., P.O. Box 981, Leadville, CO 80461. Telephone 719/486-1229; http://www.mininghalloffame.org. In addition to many unique exhibits about the history of mining, the museum includes a Mineral Room, Crystal Room, Gold Rush Room (including a 23-ounce specimen of native gold from the Little Jonny mine, Leadville), and Prospector's Cave (including the Quartz Wall, reconstructed from the Idarado mine, and a pyrite vug from the Eagle mine at Gilman).

Ouray County Museum, 420 6th Ave., Ouray, CO 81427. Telephone 970/325-4576; http://www.ouraycountyhistoricalsociety.org. This mainly historical museum includes a Mining Room and a Mineral Room that hosts an excellent display of Colorado minerals, including many specimens from mines in the San Juans and specimens from the John H. Marshall and Becky Bird collections.

Western Museum of Mining and Industry (WMMI), 1025 North Gate Rd., Colorado Springs, CO 80921; east side of 1-25 at exit 158A, Gleneagle Dr., opposite the entrance to the U.S. Air Force Academy. Telephone 719/488-0880; http://www.wmmi.org/ home.htm. The WMMI exhibits mainly emphasize mining equipment (much still operable) and the history of mining technology, but they have a modest-sized display of minerals and ore samples, many from Colorado.

[FIGURES 1-41 OMITTED]

ACKNOWLEDGMENTS

I extend sincere appreciation to Dan Kile and Tom Michalski (U.S. Geological Survey) and Jack Murphy (emeritus curator of geology, Denver Museum of Nature and Science) for reviewing and making constructive comments about this article, and to William Besse for preparing the map. The use of specimen photographs taken by Jeff Scovil and Jack Thompson is very much appreciated, and a grant to Rocks & Minerals from the Greater Denver Area Gem and Mineral Council made possible the inclusion of the many color photographs in this article. Martin Zinn Expositions also helped underwrite color publication costs.
russau
just over the state line on Douglas Creek Matt Mattson filmed a documentory on diamond indicator material found high up above Douglas Creek. i think the video is still over on Leonards video site.
ben9498
I found the article very interesting and informative.
Thank you for taking the time to post it.
toddarice
Been gone for a while. Sorry.
Julie and I know all about the state line diatremes. We have been up in that area probably 50 to 60 times, and have done good. Most of the land up there is private, the Kelsey Lake mine has been closed for a few years, and is gaurded by a herd of 'stangs. And they're mean.
Most of the diamonds in the area are small (less than 1/2 carat), but they are there. We have permission for some of it, but most, like I already mentioned, is private, or rather the roads to get there are locked and gated by the people that own land in the area. Even Chicken Park (a reallly good spot to go) was locked this year. You can file a suit, and you might win, but the land owners know that it's not worth it.
Some folks were lucky enough a few years ago to go up there a few times with Dan. But since Dan got fired and moved to Arizona, not much chance anymore. WGS just doesn't care anymore, pretty much about any rockhounding/prospecting since Dan left. But, on the bright side of things, Dan is now on the board for a major diamond company up in Canada, and has recently bought several claims in the area and up in Wyoming. Hopefully he'll taker people on expeditions again. We can only hope! Last I spoke to Vic Norris, he was also buying Vic's ruby claim in Wyoming and a couple of their diamond claims here in Colorado.
The Tonkos still own most of that whole area, but there are some places to still prospect. Also, UVing at night along Pratt, Horse, mill and willow creeks has produced some finds over the past few years, and sluicing has produced some diamonds as well as gold and accessory minerals. There is quite a bit of peridot and garnet. But the garnet and small peridot is everywhere, few cutable/mountable. We've only found trace amounts of Chrome Diopside.
I really miss the trips Dan would take us on. He could get into places us mere mortals can not. Oh, well.
Besides, breaking all the rock is really hard work. Sometimes the kimberlite is relatively soft, but most times it's hard as rock (pun intended). And sometimes (like the last trip to chicken park with the club), nobody finds anything in two days.
J.D. Dana
Nice collection. Hopefully i can find some chrome diop's some day. A minerology prof of mine (CSU good guy Malcolm McCallum) had beuutiful Chrom Diopsides rougly a quarter in size and perferctly fully formed, from SA if i remember correctly.
Bennie
wink.gif nice ones very nice CR's and that looks like a few argoyles too nice finds Tod smile.gif
Bennie
those are huge Cromium-Driopsides, a lil small for garnets But those are very white diamonds todd

about the mill creek comunity isint it illigal for them to have that fence as most of that land is national lands??? ph34r.gif laugh.gif lol they wouldnt let me through last summer they said "Theres nothing back there just a few half million dollar homes" but alot of people know theres stuff back there laugh.gif
Bennie
QUOTE (Bennie @ Dec 23 2007, 08:02 AM)
those are huge Cromium-Driopsides, a lil small for garnets But those are very white diamonds todd

about the mill creek comunity isint it illigal for them to have that fence as most of that land is national lands??? ph34r.gif laugh.gif lol they wouldnt let me through last summer they said "Theres nothing back there just a few half million dollar homes" but few of people know theres stuff back there laugh.gif

State Line district. Diamonds were found in situ in the Colorado-Wyoming region in 1975 in a Wyoming kimberlite (McCallum and Mabarak 1975). Since 1975, essentially every kimberlite in this district has yielded diamond. Even so, many of the kimberlites still have not been bulk sampled and several geophysical anomalies interpreted as blind diatremes remain inexplicably unexplored and untested. Of the bulk samples taken, ore grades range from <0.5 to 135 carats/100 tonnes with 30 to 50% gemstones and more than 130,000 diamonds have been recovered. (Early Cambrian & Early Devonian )( Hausel, 1998).Kelsey Lake Diatremes are mainly 2 kimberlites (KL1 and KL2) which had been initially mapped as the Schaffer 1, 2, 6, 7, 8, and 9 by Eggler (1967) Unfortunately, the Kelsey Lake mill was poorly designed and rejected some diamonds to its tailings as well as everything over 40 carats in weight. Thus the possibility that large diamonds were lost during the operation is likely.ome of the many unexplored anomalies in the district include:

(1) A group of distinct INPUT geophysical anomalies identified within the Wyoming portion of the district that is interpreted as blind diamond pipes these have never been drilled. Similar anomalies identified by the same INPUT survey later became part of the Kelsey Lake diamond mine. The southern portion of the district and adjacent areas has not been explored using airborne geophysics and similar blind diatremes are expected!

(2) Some additional kimberlites were recently found in the district (Pearl Creek and Sand Creek) these remain unsampled.

(3) Some very strong indicator mineral anomalies have also been found in recent years along the eastern edge of the district that indicate the presence of undiscovered kimberlites.
toddarice
Good post, Bennie.

The ones on the left are garnets and a couple of tiny chrome diopsides, diamonds in the middle and peridot on the right.

I have the last report Dan did when they did the fly-over with the magnetic imaging.
Dan did do a ton of exploring, 'til his office got pissed off that he was spending more time in Colorado than in Wyoming (that's what I was told-I don't know for sure), but I do know (because he told me so) that he explored most of that region on both sides of the line.
He also did alot of bulk sampling, as did several commercial entities. But a viable commercialy feasible pipe wasn't found at that time.
But to me, that really doesn't mean much. Kinda means the opposite to me-to me, it means that it wouldn't be worth it to them to bring in 20 million dollars worth of equipment for 10 million in diamonds. But it still means that there may be ten million worth of diamonds for us to find with our $100.00 equipment! biggrin.gif
I'll see if I can get some quotes from the CGS report (just gotta read it again) on some of the bulk sampling they did up there.

J.D.-No, it's not illegal. But it's not legal, either. They do it all over Colorado.
Some people I know who love to do the trails, have bought old mining claims just so they can keep the area open. It is sad, but a lot of these people that own property in these areas think that they are the bomb or something, I guess.
For instance, Vic Norris placed three claims on an incredible iolite deposit in the Palmer canyon area (actually south of it) of Wyoming (http://www.wsgs.uwyo.edu/metals/default.aspx).
A huge deposite. You can see some of the samples that Dan found there on the WGS page. But he had to give the fellow that owns the land surrounding that area two of the claims, just so he could access his. Of course he would have won in court, but like I mentioned before, it takes a lot of time and money.
Down closer to the owners of this site, in the Taryyalls, there are several old mines that the land owners have "blocked-off". For instance, the entrance to the bearcat mines. Used to be a great place for beryl. But you can't get in there now.

There are kimberlite pipes all ove that area. If you use flash earth and look for them, you can see them. Some right off Cherokee road.
Bennie
QUOTE (toddarice @ Dec 24 2007, 11:40 AM)
Good post, Bennie.

The ones on the left are garnets and a couple of tiny chrome diopsides, diamonds in the middle and peridot on the right.

I have the last report Dan did when they did the fly-over with the magnetic imaging.
Dan did do a ton of exploring, 'til his office got pissed off that he was spending more time in Colorado than in Wyoming (that's what I was told-I don't know for sure), but I do know (because he told me so) that he explored most of that region on both sides of the line.
He also did alot of bulk sampling, as did several commercial entities. But a viable commercialy feasible pipe wasn't found at that time.
But to me, that really doesn't mean much. Kinda means the opposite to me-to me, it means that it wouldn't be worth it to them to bring in 20 million dollars worth of equipment for 10 million in diamonds. But it still means that there may be ten million worth of diamonds for us to find with our $100.00 equipment! biggrin.gif
I'll see if I can get some quotes from the CGS report (just gotta read it again) on some of the bulk sampling they did up there.

J.D.-No, it's not illegal. But it's not legal, either. They do it all over Colorado.
Some people I know who love to do the trails, have bought old mining claims just so they can keep the area open. It is sad, but a lot of these people that own property in these areas think that they are the bomb or something, I guess.
For instance, Vic Norris placed three claims on an incredible iolite deposit in the Palmer canyon area (actually south of it) of Wyoming (http://www.wsgs.uwyo.edu/metals/default.aspx).
A huge deposite. You can see some of the samples that Dan found there on the WGS page. But he had to give the fellow that owns the land surrounding that area two of the claims, just so he could access his. Of course he would have won in court, but like I mentioned before, it takes a lot of time and money.
Down closer to the owners of this site, in the Taryyalls, there are several old mines that the land owners have "blocked-off". For instance, the entrance to the bearcat mines. Used to be a great place for beryl. But you can't get in there now.

There are kimberlite pipes all ove that area. If you use flash earth and look for them, you can see them. Some right off Cherokee road.

todd you and me need to talk!!! We both can benefit from sharing our knowlege and reports and maps my email address is quantumiil@yahoo.com (2 i's i know)
maybe we can go into the field lol

ps i have 100+ reports from hausel that guy is my idol...
russau
it sounds like you two are possible set to go have some fun! good luck!
Mrs.CP
Great information, and fantastic finds Todd! smile.gif

Here is a link to Colorado's Geological Survey's (July 1999) Rock Talk Newsletter on Colorado Diamonds. Its a PDF file.

Colorado Diamonds PDF
russau
right here in ole Missouri my geology proff showed me on a Mo map a kimberlite pipe . ive wanted go go see this in person but never have done it! maybe a side tip this year after a little research into the land owners......
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