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Sulfur isotope analyses have been performed on 64 monomineralic concentrates from 37 samples that are representative of mineralization in time and space at E1 Salvador.The hypogene sulfates (mean +10.75o; range +7.3 to +17.05o) are enriched in s4S relative to supergene sulfates (--0.75ø; --4.6 to +3.67oo) and to hypogene sulfides (--3.05ø; --10.1 to --0.37oo). Coexisting hypogene sulfides are increasingly depleted in a4S in the order molybdenite, pyrite, chalcopyrite, and bornite. The isotopic data suggest that sulfur in the supergene sulfates was largely derived from the oxidation of hypogene sulfides and that supergene "chalcocite" probably replaced hypogene chalcopyrite or bornite, but not pyrite. Isotopic temperature estimates from sulfate-sulfide fractionation pairs range from 400 ø to 570øC and are only in crude agreement with temperatures (<300 ø to >600øC) indicated by other geologic evidence. Those estimated from pyrite-chalcopyrite fractionation pairs (95 ø to 185øC) are nmch too low. Fractionation between 13 coexisting hypogene sulfate-sulfide assemblages (21 mineral pairs) defines a rather narrow band in /o•-pH-T space and suggests that [o• and pHacted as internally controlled variables throughout mineralization. Mass balance estimates of •s4Szs indicate a value of about +6 per mil for the sulfate zone and a value probably significantly heavier than 0 per mil for the entire deposit as presently exposed. The •s4S per mil values of coexisting hypogene sulfate and sulfide pairs approximate linear trends when plotted against their respective delta (/x) values. These trends suggest that Early anhydrite-chalcopyrite-bornite assemblages were formed from a sulfur reservoir having $a4Szs of approximately +1.6 per mil whereas Late anhydrite-pyritechalcopyrite assemblages formed from a reservoir +6.8 per mil $a%.s. Speculative interpretation suggests that Late sulfur was derived either from remobilization of Early assemblages below the deepest levels of exposure or from volcanic wall rocks surrounding the deposit, rather than from continued emanations from the underlying magma chamber that was the source of Early mineralization. However, at least one totally different interpretation of these data is possible. Recent experimental work by Ohmoto and Rye (1975, written and oral commun.) indicates that our $a4S per rail values for pyrite may require a correction factor, which would reduce both Early and Late sulfate-.sulfide assemblages to approximately single linear trends. This would imply that the underlying magma chamber continued to be the predominant source of sulfur ($s•Szs • +2%•) throughout the entire sequence of alteration-mineralization. The isotopic data do not show any consistent trends of s4S depletion with either paragenesis or zoning that would suggest a restricted reservoir of sulfur in the hydrothermal system. More questions than answers are provided by these data. Andesite; peripheral, 2,400 m; sericite-chlorite Andesite; peripheral, 2,400 m; sericite-chlorite "L" porphyry; central, 2,400 m; "D" v...

8•sO and/or 8D values were measured for quartz (11 samples), plagioclase (3), Kfeldspar (3), biotite (4), hornblende (1), sericite (3), chlorite (1), kaolinite (2), and pyrophyllite (1) from the porphyry copper deposit at E1 Salvador, Chile. The samples analyzed were chosen to represent the hypogene evolution from early K-silicate alteration and quartz veining to late pyritic veining and sericitic alteration to very late advanced argillic alteration, as well as supergene kaolinization. The isotopic compositions of the biotites are identical to those from most other porphyry copper deposits, and the sericite compositions are similar to those from Santa Rita. The requirements for equilibrium isotopic geothermometry are met only for unmineralized "L" Porphyry and K-silicate alteration assemblages, yielding mininmm temperatures of about 650 ø and 525øC, respectively. Temperatures estimated from various other geologic evidence are used to calculate the equilibrium isotopic compositions of hydrothermal solutions. These solutions show a distinct trend of •80 depletion and deuterium enrichment from early to late stages and from high to low temperatures. The •80 and 8D values of fluids responsible for Early K-silicate alteration assemblages are similar in isotopic composition to magmatic waters but are enriched in deuterium relative to the later unmineralized "L" Porphyry even though it is petrologically similar to the earlier mineralized porphyries. Later fluids are dominantly meteoric waters enriched in •sO by reaction with the host rock. Late and presumably shallow advanced argillic assemblages developed from acid geothermal waters of meteoric origin that were enriched in deuterium and •80 by near-surface evaporation processes. There was possibly some mixing between these fluids and the deeper meteoric-hydrothermal fluids. The similar isotopic compositions of both meteoric and magmatic waters and the variety of possible processes modifying their isotopic compositions prevent a quantitative analysis of the relative proportions of each at the different stages in the evolution of the hydrothermal fluids.

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Chuquicamata, in northern Chile, is the world's greatest copper orebody. It was controlled, from the initial intrusions (probably at 36-33 Ma) through mineralization (last major hydrothermal event at 31 Ma) to postmineral brecciation and offset, by the West fault system. East porphyry, West porphyry, Banco porphyry, and Fine Texture porphyry make up the Chuqui Porphyry Complex. East porphyry, the dominant host rock, has a coarse, hypidiomorphic-granular texture. Intrusive contacts between most porphyries have not been found, but early ductile deformation, subsequent pervasive cataclastic deformation, and faulting affects all of the rocks and makes recognition of intrusive contacts very difficult.Potassic alteration affects all porphyries, comprises partial K feldspar and albite replacement of plagioclase, and more widespread biotite replacement of hornblende, with igneous texture largely preserved. It is accompanied by granular quartz and quartz-K feldspar veinlets, which contain only trace disseminated chalcopyrite ± bornite remains from this early stage. Fine-grained quartz-K feldspar alteration, with destruction of biotite and apparently following albitization of plagioclase, accompanies strongest cataclastic deformation and destruction of igneous texture. A band of quartz-K feldspar alteration, up to 200 m wide and 1,500 m long, lies along the southward extension of Banco porphyry dikes and is the locus of the bornite-digenite center of the sulfide zoning pattern. This passes east through chalcopyrite-bornite to chalcopyrite-pyrite as sulfide abundance fades out. Sulfides in quartz-K feldspar alteration are abundant only where there is intense crackle brecciation. Propylitic alteration is superimposed on biotitic alteration at the eastern edge of the deposit, but there is no pyritic fringe. Westward, this zoning is interrupted by the superposition of pyritic main-stage veins with pervasive quartz-sericite. Veins of quartz-molybdenite, up to 5 m wide and cutting all porphyries, were emplaced between the early and the main stages. These veins and early-stage quartz veins are commonly segmented and sheared, with fine recrystallization of quartz that eliminates all original fluid inclusions. It is not clear whether quartz-K feldspar alteration was formed later or earlier than quartz-molybdenite veins.Main-stage veins were focused along a structural zone adjacent to the West fault. This stage is distinctly younger than early-stage mineralization, although it occupies many of the same structures and may involve massive remobilization of earlier mineralization. It may represent a more brittle and much shallower environment, which followed significant erosion of the upper parts of the early mineralization system. Main-stage veins with quartz, pyrite, chalcopyrite, and bornite were formed during dextral shear of the West fault system. The last mineralization of the main stage was enargite, digenite, covellite, pyrite, and minor coarse sphalerite, along with sericite, and locally alunite but only local traces of pyroph...