Cobalt-rich characteristics and existing problems of porphyry gold-copper deposit: A case study of Jinchang deposit in Heilongjiang Province

Abstract

<p indent="0mm">Cobalt is a strategic critical metal and China relies on foreign sources for 95% of its cobalt supply. With the promotion of new energy vehicles and the application of cobalt in power batteries, it is predicted that the consumption of cobalt in 2025 and 2035 will be twice and five times that of today. At present, most of cobalt resources in the world are provided by two types of deposits: Sediment-hosted stratiform copper-cobalt deposits and nickel-cobalt laterite deposits, accounting for about 80% of the terrestrial cobalt resources. China lacks these two types of deposits. The main types of deposits that produce cobalt resources in China are magmatic sulfide copper-nickel deposits and hydrothermal cobalt-bearing deposits (including skarn deposit, volcanic massive sulfides deposit and metasedimentary rocks hosted deposit, etc.). Cobalt is enriched in many skarn deposits related to intermediate rock. Some cobalt-rich skarn deposits are considered to be porphyry-skarn composite deposits. It is generally believed that most ore-forming metals and fluids related to porphyry-skarn systems were derived from deep magma chambers. Therefore, porphyry deposits closely related to skarn deposits may also have the potential to be rich in cobalt. To date, a “typical” cobalt-rich porphyry deposit has not been discovered, hampering study of cobalt enrichment mechanisms in magmatic hydrothermal or porphyry systems. However, the Jinchang gold-copper deposit, Heilongjiang Province, is a large-scale porphyry gold deposit comprising breccia, fracture-controlled, and veinlet disseminated ore features with clear cobalt enrichment in the breccia (Co content &gt; 0.01wt%). By estimating the proportion of cobalt minerals in sample and the cobalt content in cobalt minerals, the cobalt content of the ore can be calculated as approximately 0.08%. The content of cobalt in massive copper ore (Cu content &gt; 15wt%) and disseminated copper ore (Cu content &lt; 5wt%) was measured respectively. The average cobalt content of the two types of samples was 0.072wt% ± 0.028wt% (1<italic>σ</italic>, <italic>n</italic> = 8) and 0.054wt% ± 0.042wt% (1<italic>σ</italic>, <italic>n</italic> = 7), respectively. Accordingly, the cobalt content of Jinchang deposit reaches or exceeds the industrial grade of sulfide cobalt ore (Co content &gt; 0.03wt%−0.06wt%) and testifies to the huge potential for cobalt mineralization and enrichment in this porphyry deposit. We have comprised a database of pyrite cobalt content for typical porphyry gold-copper deposits (Beiya and Jinchang), porphyry copper-gold deposits (Duobuza), porphyry copper deposits (Dexing and Baogutu) and porphyry copper-molybdenum deposits (Qulong) in China. The data show that the porphyry gold and gold-copper deposit have the highest cobalt content. The variation of cobalt content may be related to the gradual decrease in the proportion of mantle-derived magma contribution. Due to the small number of statistical samples, there may be great uncertainty in this inference, so more research on cobalt-rich porphyry deposits needs to be done. Future research on the characteristics and mechanisms of cobalt enrichment in the Jinchang porphyry gold-copper deposit should focus on: (1) Identifying different cobalt minerals and cobalt-bearing minerals, and identifying substitution mechanisms; (2) clarifying the specific contribution of mantle-derived magma to the enrichment of gold, copper, cobalt and other metal elements in the deposit; (3) revealing the migration behavior of cobalt in moderate to high temperature magmatic hydrothermal fluids; (4) constraining the main factors controlling cobalt precipitation. A detailed study of the Jinchang cobalt-rich porphyry deposit will help reveal the geochemical behavior and enrichment mechanism of cobalt in porphyry deposits, and provide a typical example for further study of porphyry cobalt-rich deposits.

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