Lithocaps are permeable lithologic horizons that are altered to residual quartz with halos of quartz-alunite and other advanced argillic minerals; they are formed by acidic condensates of magmatic volatiles from underlying intrusions. Lithocap alteration forms near the surface at the same time as potassic alteration of underlying porphyry deposits, due to the linked vapor and hypersaline liquid, respectively. Lithocaps are barren in metals on formation, but some become mineralized with Au and Cu (the latter as high sulfidation-state sulfides).
This course will discuss the formation of lithocaps, and present their characteristics and alteration zoning, plus mineralization in some cases (caused by ascent of fluid related to the white mica-chlorite overprint of intrusions at depth). Variable relationships of lithocaps to underlying intrusions and porphyry Cu±Au deposits, and the mineralogical transition at the base of lithocaps to the tops of porphyry mineralization, will be examined, stressing features to assist exploration and assessment.
It will be held in English with simultaneous translation.