PGE geochemical constraints on the origin of the Ni-Cu-PGE sulfide mineralization in the Suoi Cun intrusion, Cao Bang province, Northeastern Vietnam

Abstract

The Permian (266-262 Ma) Suoi Cun intrusion in the Song Hien Rift Zone (NE Vietnam) consists of a sulfidebearing mafic-ultramafic unit and a sulfide-free mafic unit. The Cu-Ni-PGE mineralization is represented by disseminated sulfides throughout the sulfide-bearing unit containing 0.5 wt.% Ni,~0.05 wt.% Cu, and~0.2 ppm PGE. The sulfide schlieren have a limited distribution and contain~2.6 wt.% Ni, 0.5 wt.% Cu, and~2.6 ppm PGE. The Suoi Cun rocks containing disseminated sulfides display moderately fractionated mantle-normalized PGE patterns with positive Pd and negative Ru anomalies. In contrast, the sulfide schlieren show enrichment in Ru with lower contents of other PGE except Pd. The low Cu/Pd ratios (1,385-11,529) throughout the intrusion indicate that all sulfides were separated from a PGEundepleted magma as a result of a single sulfide segregation event. We suggest that sulfides segregated from Mg-rich basaltic magmas in a deep-seated magma chamber due to crustal contamination with country rocks. Then, the sulfide liquid along with early crystallizing olivines and Cr-spinels were pushed out upwards into an upper magma chamber by new pulses of magma. Two processes were important for understanding the PGE distribution: 1) fractionation of the sulfide liquid gave rise to PGE distribution observed in the disseminated ore and, 2) the interaction of oxidized silicate melts with the sulfide liquid was the responsible for the low PGE contents in the sulfide schlieren due to PGE transfer from the oxidized sulfide liquid to the silicate melt.

PGE-Cu-Ni Mineralization of Mafic-Ultramafic Massifs of the Khangai Upland, Western Mongolia

“…Exsolution of hexagonal pyrrhotite with enclosed troilite lamellas is a low-temperature process (from~300 to 100 • C and lower), due to the subsolidus transformations of the initial high-temperature monosulfide solid solution (MSS) [65]. Such exsolutions were found in the ores of Cu-Ni-PGE occurrences, such as Kingash in Siberia [66], the Suoi Cun intrusion in Northeastern Vietnam [67]. The Fe content in pentlandite decreases with increasing Ni content (Figure 10) during the change of assemblages in the troilite-hexagonal pyrrhotite series.…”

Petrology of Ortsog-Uul peridotite-gabbro massif in Western Mongolia

“…Many mafic-ultramafic layered sulfide-bearing intrusions of the southeastern Siberian Region [1,2], the Vietnam [3], the China [4], and the Mongolia [5] is studied recently. A brief summary of the Ortsog-Uul massif based on previous geological reports in Russian by Izokh et al [6].…”