Occurrence and enrichment of cobalt in Jinchang cobalt.rich porphyry deposit,Heilongjiang Province

Porphyry deposits, a type of typical magmatic.hydrothermal deposits,have provided large quantities of copper, molybdenum,gold and other critical minerals such as rhenium,selenium and tellurium. Up to now,none of a typical cobalt.rich porphyry deposit is reported in the world. The Jinchang deposit in Heilongjiang Province is a large porphyry gold-copper deposit with 76 tons of gold and 4,683 tons of copper. In this paper,the samples from the Jinchang deposit are studied in aspects of petrology, mineralogy and geochemistry. Handheld X.ray fluorescence analysis results reveal significant cobalt enrichment (cobalt content:237 x 10 (- 6)similar to 5256 x10 (- 6))in the J0 breccia ore. Electron microprobe analysis shows that cobalt is mainly enriched in pyrite in the form of isomorphism,and to a lesser extent in siegenite and cobaltite. The pyrites are divided into three types according to their occurrences and mineral assemblages. Type I pyrites are euhedral grains formed in the early stage coexist with magnetite,which can be further divided into two subtypes:cobalt uniform enrichment (I-1)and core cobalt enrichment (I-2). Type. pyrites are subhedral to euhedral grains which formed at a later stage and are mostly surrounded by chalcopyrite,quartz and carbonate minerals,which can be further divided into three subtypes:rim cobalt enrichment (I-1),mantle cobalt enrichment (I-2)and containing cobalt zones (I-3). Type. pyrites are subhedral to euhedral grains which occurred in late quartz.pyrite veins,containing quartz or silicate mineral inclusions. The samples containing type I pyrites have the highest cobalt content (1800 x10 (- 6) similar to 5200 x10 (- 6)),those containing type. pyrites have moderate cobalt content (800 x 10 (-6) similar to 1600 x 10 (- 6)),while those containing type. pyrites have a relatively low cobalt content (240 x10 (- 6) similar to 360 x10 (-6)). Samples formed in the early stage have higher cobalt contents,so cobalt enrichment may mainly occur in the early stage of deposit formation. It is noteworthy that the ore containing type I pyrite has the most potential for cobalt resource exploitation. Based on the S.H.O.Re.Os.He isotopic studies on the Jinchang deposit,it is considered that the cobalt in Jinchang deposit is likely to be originated from deep mantle.derived magma. This case study provides a typical example for cobalt.rich porphyry deposits