How Are Porphyry Copper Deposits Formed
Porphyry copper deposits usually refer to rich communities of disseminated veinlet disseminated and veinlet copper and molybdenum-copper components associated with porphyritic granitoids.И.Г.Pavlova put forward 10 characteristics of porphyry copper deposits that can be distinguished from other endogenous deposits:
(1) with the characteristics of network veinlets;
(2) the composition of the major metallic minerals (pyrite, magnetite, chalcopyrite, pyroxene, and in some deposits porphyry, thioarsenite, and pyrite) and the associated nonmetallic minerals (quartz, sericite, potassium feldspar, biotite, kaolinite, etc.) is stable;
(3) the average content of copper is relatively low in primary ores (0.3-0.8%), but significantly higher in oxidized ores (1-1.5%), while the distribution of molybdenum in primary oxidized ores is relatively uniform (0.005-0.05%). In this case, the ratio of copper to molybdenum in ores varies greatly, forming a series of important copper, copper-gold and copper-molybdenum deposits.
(4) mineralization and mainly neutral porphyry intrusions (granodiorite porphyry, quartz monastic porphyry), and a few slightly acidic (granoporphyry,
It is spatially related to the basic-biased intrusive body (diorite porphyry).
(5) mineralization may occur directly in the porphyry intrusive body, or in the surrounding rocks -- volcanic rocks, intrusive rocks and metamorphic rocks in the external contact zone immediately adjacent to the intrusive body;
(6) ore bodies are developed in the zone where hydrothermal alteration rocks are widely found. The alteration rocks are serician-quartzite, biomica-potassium feldspar, argillaceous and qingpanrock-type metasomatism rocks.
(7) according to the maximum value of metallic elements and the main symbiotic non-metallic minerals (2), the stable zonation in orebodies and hydrothermal rocks can be written in the following order.Fe3+ one Mo(Cu) one Cu(Mo) one Cu(Ag) one Fe2+(Au) one Pb one Zn (Au, Ag);
(2) biotite - potassium feldspar, sericite, quartz, montmorillonite, kaolin, qingpanyan
(8) the huge reserves of the deposit guarantee the large-scale mining of ore, low cost and the possibility of open pit mining.
(9) the occurrence of rich ore related to oxidation formed secondary sulfide enrichment zone covering poorer primary ore
(10) the porphyry copper deposits were formed at different developmental stages in the geosynclinal fold area (plate active edge).It can be formed before the main stage of the fold (in the island arc stage) with the magmatism of the geosyncline, and related to the porphyry intrusions and sub-volcanic rocks in the orogenic stage and activation stage (intraplate fault zone).
In the modern classification of many porphyry copper deposits, the following features are utilized, not only in terms of individual features, but also in terms of combinations of features:
(1) location of geotectonics and paleotectonics;
(2) composition of mineral-bearing porphyry facies formed by mineral-bearing magmatic formation;
(3) crust thickness and composition invaded by mineral-bearing magma formation;
(4) by R.H.The occurrence of ore bodies in the porphyry copper system classified by silito;
(5) the formation depth of ore-bearing magmatic rock mass;
(6) the existence of breccia tube;
(7) the composition of the main ore and the ore with an admixture;
(8) zonal characteristics of metal ore;
(9) composition and zonation of hydrothermal altered rocks;
(10) ore-bearing intrusive bodies and morphological characteristics of ore-bearing bodies.