CONDITIONS OF FORMATION OF THE LATE PERMIAN CAO BANG PGE-Cu-Ni-BEARING LHERZOLITE-GABBRONORITE-DOLERITE COMPLEX ( northeastern Vietnam )
P.A. Balykin, G.V. Polyakov, Tran Trong Hoa*, A.V. Lavrenchuk, A.E. Izokh, Ngo Thi Phuong*, A.I. Glotov, Hoang Huu Thanh*, T.E. Petrova, and E.A. Vasyukova
Institute of Geology and Mineralogy, Siberian Branch of the RAS,
3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
* Institute of Geosciences, Vietnamese Academy of Sciences and Technologies,
Hoang Quoc Viet, Ngia Do, Cau Giei, Hanoi, Vietnam
Keywords: Lherzolite-gabbronorite-dolerite complex, initial picrobasalt magma, PGE-Cu-Ni mineralization, initial picrobasalt magma, northeastern Vietnam
Pages: 821-834
Abstract
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 (f Ol = 16-18%), magnesium diopside-augite (f MP = 18-20%), and low-alumina bronzite (f RP = 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
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