Publication Summary
Issue ID: P2014-01-09
Title: Mineralogy of sulphide, arsenide, and platinum group minerals from the DJ/DB Zone of the Turnagain Alaskan-type ultramafic intrusion, north-central British Columbia
Author(s): Jackson-Brown, S., Scoates, J.S., Nixon, G.T., Ames, D.E.
Series Name: Paper
Publication Year: 2014
Larger Work Citation: in Geological Fieldwork 2013, B.C. Ministry of Energy and Mines, Paper 2014-01
NTS Map Sheet(s): 104I/07
Place Keyword(s): British Columbia
Lat/Long (NSWE): 58.52, 58.45, -128.94, -128.78
Theme Keyword(s): platinum group elements, platinum-group minerals, ultramafic intrusion, Alaskan-type, Turnagain intrusion
The Turnagain intrusion (ca. 190 Ma) is an Alaskan-type, ultramafic body emplaced in an orogenic setting that is host to a significant nickelcobalt resource (865 Mt at 0.21% per tonne Ni and 0.013% per tonne Co). The 24 km2 intrusion comprises a suite of ultramafic rocks including dunite, wehrlite, clinopyroxenite, and hornblendite with minor late-stage dioritic intrusions and inclusions of hornfelsed country rocks. Soil geochemistry and drilling led to the discovery of an area of copper and platinum group element (PGE) enrichment in a previously underexplored area of the intrusion, the DJ/DB zone, 2.5 km northwest of the nickel resource. We conducted a detailed mineralogical investigation to assess the range of compositions and textures of platinum group minerals (PGM) and associated sulphides in the DJ/DB zone. Mineralized clinopyroxenites and hornblendites, typically with less than 5 vol.% sulphide, contain mainly chalcopyrite and pyrrhotite with minor pyrite and pentlandite, and host a variety of arsenides, arsenic-antimony sulphides, and PGM. Arsenic and antimony-bearing phases are typically related to chalcopyrite and include cobaltite (CoAsS), nickeline (NiAs), gersdorffite (NiAsS), ullmannite (NiSbS) tucekite (Ni9Sb2S8), and hauchecornite (Ni9Bi(Sb,Bi) S8). Identified PGM are predominantly sperrylite (PtAs2) and sudburyite (PdSb), with minor Pd-melonite [(Ni,Pd)Te2], hongshiite (PdCu), testibiopalladite [PdTe(Sb,Te)], and genkinite [(Pt,Pd)4Sb3]. Platinum- and palladium-bearing minerals commonly form equant 1 - 40 Ám grains, within chalcopyrite, pyrrhotite, pentlandite, cobaltite and silicates. Sperrylite and sudburyite also occur as veinlets within and as partial rims (~ 1 - 10 Ám thick) on the periphery of base metal sulphides. The textural paragenesis and mineral chemistry of PGM and associated minerals in the DJ/DB zone of the Turnagain intrusion are compared to those observed from other Alaskan-type intrusions. These findings highlight the potential for finding PGE-mineralized units in other Alaskan-type intrusions in the Canadian Cordillera and older orogenic ultramafic-mafic intrusions elsewhere in Canada.