Keep in mind, the opinions on this site are for the most part speculation and are not necessarily the opinions of the company WITHOUT PREJUDICE
http://goldminingandprospecting.blogspot.ca/2011/03/geology-of-hydrothermal-quartz-veins.html
http://www.miningandmetallurgy.com/metallurgy/gold-veins-near-surface
http://www.miningandmetallurgy.com/gold/html/where_does_gold_occur__where_a.html