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GEOREF RECORD

The evolution and structural modification of the supergiant Mitchell Au-Cu porphyry, northwestern British Columbia

Gayle E. Febbo, Lori A. Kennedy, JoAnne L. Nelson, Michael J. Savell, Michelle E. Campbell, Robert A. Creaser, Richard M. Friedman, Bram I. van Straaten and Holly J. Stein
The evolution and structural modification of the supergiant Mitchell Au-Cu porphyry, northwestern British Columbia
Economic Geology and the Bulletin of the Society of Economic Geologists (March 2019) 114 (2): 303-324

Abstract

The calc-alkalic Mitchell Au-Cu-Ag-Mo porphyry deposit, hosted in intrusive rocks of the Stikine volcanic arc terrane of northwestern British Columbia, is the largest undeveloped gold resource in Canada, with 40.72 Moz of contained gold. It lies within the KSM trend, a 12-km-long linear porphyry array in the Sulphurets district. It is genetically related to Early Jurassic Sulphurets stocks: phase 1 diorite to monzodiorite hosts Cu-Au mineralization in potassic assemblages (stage 1), a phase 2 granodiorite plug cores a molybdenum halo (190.3 + or - 0.8 Ma, 191.3 + or - 0.7 Ma; Re-Os, molybdenite) that is accompanied by phyllic alteration (stage 2), and a poorly mineralized phase 3 diorite plug temporally overlaps with quartz-pyrophyllite alteration at shallow levels (stage 3). Two deformation events (D (sub 1) and D (sub 2) ), attributed to orogen-scale mid-Cretaceous transpression, structurally modified Mitchell. D (sub 1) deformation, expressed as steep E-striking pressure solution cleavage (S (sub 1) ) and related W-plunging folded veins (F (sub 1) ), is heterogeneously developed as a function of alteration type. D (sub 2) is divided into two progressive events: D (sub 2a) , defined by N-plunging, folded veins (F (sub 2a) ), and D (sub 2b) , defined by E-vergent thrust faults, including the Mitchell thrust fault, which offsets the updip continuation of Mitchell (the Snowfield deposit, 192.0 + or - 1.0 Ma, 191.1 + or - 0.8 Ma; Re-Os, molybdenite) approximately 1,600 m to the east-southeast. Host structures for the KSM trend may have been long-lived, N-striking basement lineaments that provided transcrustal magma and fluid pathways. East-trending intrusions, hydrothermal veins, alteration and metal distribution at Mitchell are attributed to subsidiary E-striking cross faults. These original anisotropies in turn influenced the geometry of Cretaceous faults and flattening domains within the deposit.


ISSN: 0361-0128
EISSN: 1554-0774
Coden: ECGLAL
Serial Title: Economic Geology and the Bulletin of the Society of Economic Geologists
Serial Volume: 114
Serial Issue: 2
Title: The evolution and structural modification of the supergiant Mitchell Au-Cu porphyry, northwestern British Columbia
Affiliation: University of British Columbia, Mineral Deposit Research Unit, Vancouver, BC, Canada
Pages: 303-324
Published: 201903
Text Language: English
Publisher: Economic Geology Publishing Company, Lancaster, PA, United States
References: 62
Accession Number: 2019-032106
Categories: Structural geologyEconomic geology, geology of ore deposits
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables, sects., geol. sketch maps
N54°00'00" - N59°00'00", W130°00'00" - W127°00'00"
Secondary Affiliation: British Columbia Geological Survey, CAN, CanadaSeabridge Gold, CAN, CanadaOregon State University, College of Earth, Ocean and Atmospheric Sciences, USA, United StatesUniversity of Alberta, Department of Earth and Atmospheric Sciences, CAN, CanadaColorado State University, AIRIE Program, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Abstract, Copyright, Society of Economic Geologists. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201917
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