Abstract: The composition and mechanism of intrusion and accumulation of “sulfide slurry” are still under debate in the study of magmatic copper-nickel sulfide deposits. In this report, based on the idea of the newly proposed “magmatic conduit metallogenic system”, we studied the ore-bearing olivine-gabbronorite in the Talnakh Cu-Ni sulfide deposit in Norilsk, Russia. We found two types of main rock-forming minerals that have significantly different trace elemental compositions. Here, we focus on the characteristics of plagioclase. Based on the distribution pattern of trace elements, all plagioclase can be divided into two types. The type I plagioclase consists of albite-bytownite and is highly enriched in LILEs and LREEs and largely depleted in HFSEs. It is assembled as sulfide droplet and obviously altered by the fluid, indicating the sulfide droplets are likely filled with fluid. The type II plagioclase is enriched in LREEs, largely depleted in HFSEs, and consists of andesine-bytownite. It shows weak alteration by fluid, suggesting that it is formed by normal crystallization. Thus, we believe that “sulfide slurry” contained a large amount of fluid during the intrusion process and should be called “melt-fluid”. This study provides new evidence to support the theory that fluid activities played an important role in the enrichment and migration of sulfides in Cu-Ni sulfide deposits.

Key words: Talnakh Cu-Ni sulfide deposit, magmatic conduit metallogenic system, plagioclase, fluid process