Why do you think it was quarried? I don't see any signs of rockwork in your picture.
It looks like the typical quartz
blowout. When these blowouts occur in granite the
natural swelling of the granite tends to break up the quartz it surrounds and cause the collapse.
The quartz could have been carried off by humans for building stone or silica sand but more likely the quartz is buried under the resulting eluvial mass from the collapse of the intrusion.