Late Permian PGE-Cu-Ni-bearing lherzolite-gabbronorite-dolerite and dolerite-kongadiabase-granophyre intrusions of the Song Hien rift structure in northeastern Vietnam (Cao Bang complex) were formed synchronously with the Emeishan traps of the Yangtze Platform. Massifs of this complex are made up of rocks of two series: lherzolite-picrite-picrodolerite-melanogabbro and kongadiabase-dolerite-gabbronorite. The first, essentially ultramafic, series is dominated by plagioperidotites and picritoids composed of labradorite-bytownite (An66–70), chrysolite (fOl = 16–18%), magnesium diopside-augite (fMP = 18–20%), and low-alumina bronzite (fRP = 20–22%). They are associated with Pd-dominated PGE-Cu-Ni mineralization. In the sulfide phase of picrite from the endocontact zone of the Suoi Cun massif the contents of noble metals are as follows: 7.67 ppm Pt, 18.58 ppm Pd, 26.55 ppm Au, and 32.44 ppm Ag. Model calculations show that this massif was produced by the single intrusion of a high-Al picrobasalt magma crystallized at 1260–1090 °C and 1–3 kbar, with oxygen activity close to the WM buffer.
The Cao Bang complex and other occurrences of Permian-Triassic ultramafic-mafic magmatism of northern Vietnam and southern China including traps of the Emeishan Province are related to a Permian-Triassic mantle plume similar to the Siberian plume. The data obtained indicate that this complex is promising for PGE-Cu-Ni mineralization of the Noril’sk type.
