Drummond, DA and Cloutier, J and Boyce, AJ and Prave, AR, Petrogenesis and geochemical halos of the amphibolite facies, Lower Proterozoic, Kerry Road volcanogenic massive sulfide deposit, Loch Maree Group, Gairloch, NW Scotland, Ore Geology Reviews, 124 Article 103623. ISSN 0169-1368 (2020) [Refereed Article]
The Palaeoproterozoic Kerry Road deposit is one of the oldest examples of volcanogenic massive sulfide (VMS) mineralization. This small VMS deposit (∼500,000 tons grading at 1.2% Cu, 3.5% Zn) is hosted in amphibolite facies mafic-siliciclastic units of the c. 2.0 Ga Loch Maree Group, Scotland. Sulfide mineralization consists of pyrite and pyrrhotite with subordinate chalcopyrite and sphalerite, occurring in disseminated, vein and semi-massive to massive textures.
The deposit was highly deformed and metamorphosed during the c. 1.8–1.7 Ga Laxfordian Orogeny. Textural relationships of deformed sulfide minerals, related to early Laxfordian deformation (D1/D2), indicate initial high pressure-low temperature (100 MPa, 150 °C) conditions before reaching peak amphibolite facies metamorphism, as evident from pyrrhotite crossing the brittle/ductile transition prior to chalcopyrite. Late Laxfordian deformation (D3/D4) is marked by local retrograde greenschist facies at low pressure and temperature (<1.2 MPa, <200 °C), recorded by late red sphalerite remobilization. δ34S values from all sulfide minerals have a homogeneous mean of 0.8 ± 0.7‰ (n = 21), consistent with interaction of hydrothermal fluids in the host oceanic basalt-island arc setting envisaged for deposition of the Loch Maree Group.
Microprobe analyses of amphiboles record evidence of the original alteration halo associated with the Kerry Road deposit, with a systematic Mg- and Si- enrichment from ferrotschermakite (∼150 m) to Mg-hornblende (∼90 m) to actinolite (0 m) on approach to the VMS deposit. Furthermore, whole rock geochemistry records a progressive enrichment in Si, Cu, Co, and S, and depletion in Al, Ti, V, Cr, Y and Zr with proximity to the VMS system. These elemental trends, together with amphibole geochemistry, are potentially useful exploration vectors to VMS mineralization in the Loch Maree Group, and in similar highly deformed and metamorphosed terranes elsewhere.
|Item Type:||Refereed Article|
|Keywords:||Kerry Road deposit, volcanogenic massive sulfide, Lewisian complex, alteration, S isotopes, sulfide deformation|
|Research Division:||Earth Sciences|
|Research Field:||Igneous and metamorphic petrology|
|Objective Division:||Mineral Resources (Excl. Energy Resources)|
|Objective Group:||Mineral exploration|
|Objective Field:||Copper ore exploration|
|UTAS Author:||Cloutier, J (Mr Jonathan Cloutier)|
|Deposited By:||CODES ARC|
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