Geochemical and Geochronological Discrimination of Biotite Types at the Detour Lake Gold Deposit, Canada

Renelle Dubosq,Alfredo Camacho,David Schneider,Christopher Lawley

doi:10.3390/min9100596

Abstract

The Detour Lake deposit is at a faulted contact between mafic volcanic and siliciclastic to volcaniclastic rocks, differing from other orogenic Au deposits in the dominantly greenschist facies Abitibi region, by possessing amphibolite facies assemblages. Consequently, typical indicator minerals for mineralization, like secondary biotite, may not be useful for locating ore zone, due to the challenge of distinguishing hydrothermal versus metamorphic and magmatic phases. Herein, geochemical and 40Ar/39Ar geochronological data are presented for biotite from mineralized and barren (distal) magmatic rocks to characterize potential geochemical and geochronological variations between biotite types. Petrological observations reveal four biotite types: (1) Biotite hosted in mineralized, sulphidized quartz-calcite veins, (2) halo biotite at the margins of the aforementioned veins; (3) host rock biotite defining the foliation within the mafic volcanic rocks of the deposit; and (4) biotite defining the foliation within the barren meta-plutonic host rocks. Chemical analysis reveals a lower Ti- and higher Mg-content of mineralized biotite types, indicative of secondary hydrothermal processes. 40Ar/39Ar ages for all biotite types (2600–2390 Ma) post-date the main syn-deformation mineralization event at Detour Lake (≤2700 Ma). These results suggest chemical variations within biotite are due to a post-mineralization hydrothermal event, thus biotite should be used cautiously as a vector for gold mineralization in amphibolite facies terranes.

Highlights

Previous studies of orogenic Au deposits in the Archean Superior Province, including the CanadianMalartic deposit [1,2] and the Mouska deposit [3], have highlighted the importance of biotite as indicator minerals for Au mineralization and for constraining the paragenesis of mineralization
We suggest that new biotite ages may have dated younger, or possibly a series of younger, hydrothermal events that are unrelated to Au mineralization
Our petrographic observations suggest four distinct types of pre to syn-D2 biotite (1–3 mineralized; 4 barren): (1) vein biotite in pre- to syn-D2 vein sets ranging from fine- to coarse-grained, subhedral to euhedral crystals; (2) medium-grained euhedral halo biotite that parallel the pre- to syn-D2 vein margins; (3) host rock biotite ranging from very fine-grained to coarse-grained, anhedral to euhedral crystals; and (4) very fine to coarse-grained, anhedral to euhedral biotite, defining the foliation within the barren meta-plutonic host rocks distal to the deposit

Summary

Introduction

Previous studies of orogenic Au deposits in the Archean Superior Province, including the CanadianMalartic deposit [1,2] and the Mouska deposit [3], have highlighted the importance of biotite as indicator minerals for Au mineralization and for constraining the paragenesis of mineralization. Northeastern Ontario, a late, post-metamorphic biotite-bearing hydrothermal alteration mineral assemblage related to auriferous veins and broader mineralized zones, with disseminated Au, was identified [4]. A previous study observed an extensive biotite-rich halo surrounding the main mineralized zone in the hanging wall of the Detour Lake deposit, resulting in mafic volcanic host rocks with a purple-maroon appearance [5]. On the basis of these field relationships, hydrothermal biotite was suggested to be an important visual indicator mineral for the exploration and production geology teams to target and delineate Au ore zones. ± ilmenite) [5], which obscures the relationship between secondary biotite and Au mineralization. Relationship between secondary biotite and Au mineralization. Differentiating metamorphic and Differentiating metamorphic and secondary hydrothermal biotite is challenging within secondary hydrothermal biotite is challenging within low-grade disseminated Au ore low-grade disseminated

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Discussion

Conclusion