Geology Reference
In-Depth Information
Fig. 4.7 Diagram of the upper part of a granitic pluton in a volcanic edifice, the location of many
porphyry copper deposits (Modified from Sillitoe 2010 )
upper portions of the intrusion and in surrounding rocks. Original sulfide minerals
are pyrite, chalcopyrite, bornite, and molybdenite. Gold is often in native form and
is found as tiny blobs along borders of sulfide crystals, or it occurs in sulfosalts like
tetrahedrite. Most of the sulfides occur in veins or plastered on fractures and most
are intergrown with quartz or sericite. In many cases, the deposits have a central
low-grade zone enclosed by 'shells' dominated by bornite, then chalcopyrite, and
finally pyrite, which may be up to 15% of the rock. Molybdenite distribution is
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