The tops and bottoms of porphyry copper deposits: Economic Geology, v

Although it is now widely accepted that porphyry copper deposits consist of zonally arranged shells of alteration and mineralization centered on high-level, calc-alkaline stocks, the nature of their uneconomic upward and downward extensions remains un-documented. This paper attempts to characterize these upward and downward ex-tensions and to integrate the resulting concepts into a hypothetical model for complete porphyry copper systems. Examples from Chile, Argentina, and elsewhere are used to aid in the substantiation of the model. Programs of exploration for porphyry ore de-posits can clearly benefit from the application of a model of this sort. A typical porphyry copper-bearing stock is inferred to grade downward into stock-work mineralization and potassium silicate alteration in a phaneritic intrusive, which in turn is transitional downward to an essentially unaltered pluton of considerably larger dimensions than the stock. Porphyry copper deposits are normally located in the basement beneath a comagmatic volcanic pile, which is transected by a column of hydro-thermal alteration representing the upper parts of the porphyry copper system. Thi