Geological Setting of Volcanogenic Massive Sulphide Occurrences in the Middle Paleozoic Sicker Group: Southeastern Cowichan Lake Uplift, Southern Vancouver Island, British Columbia MDRU Tyler Ruks and Jim Mortensen Mineral Deposit Research Unit UBC Mineral Deposit Research Unit, Department of Earth and Ocean Sciences, University of British Columbia, 6339 Stores Rd., Vancouver B.C., V6T 1Z4; Phone: 604.822.6136; Email: [email protected], [email protected] Abstract 441000.000000 442000.000000 443000.000000 444000.000000 445000.000000 446000.000000 447000.000000 Legend Volcanogenic strata of the mid-Paleozoic Sicker Group on Vancouver Island host the world- 0 0 0 0 0 1,000 500 0 1,000 Meters LEGEND 0 0 0 class Myra Falls volcanogenic massive sulphide (VMS) deposit, as well as numerous other VMS 0 0 0 0 . INTRUSIVE ROCKS . deposits and occurrences, many of which are located in the Big Sicker Mountain area, in the 0 0 0 0 southeast portion of the Cowichan uplift. Three of these deposits, the Lenora, Tyee and Richard III 0 LATE TRIASSIC 0 5 5 (MINFILE occurrences 092B 001, 002, 003) have seen limited historical production, with the Lara 1 75 1 4 SILLS AND DYKES: diabase and gabbro 4 deposit (MINFILE occurrence 092B 129), farther to the northwest, containing a significant drill- 5 ç 5 indicated resource. Logging activity in the Mount Sicker area over the past decade has provided 05M-355 VOLCANIC AND SEDIMENTARY ROCKS abundant new outcrops. This, coupled with a lack of absolute age control for rocks in this area, has 84 UPPER CRETACEOUS prompted a re-examination of Sicker Group stratigraphy and the geological setting of VMS ç mineralization in the region. Buttle Lake Group 81 NANAIMO GROUP: mudstone, sandstone, 05M-357 Geological mapping (Massey and Friday, 1987; this study) suggests that the Big Sicker ç and boulder conglomerate 0 0 0 0 Mountain area is underlain mainly by deformed mafic to felsic volcanic and volcaniclastic rocks of 0 0 0 MIDDLE DEVONIAN 0 Campbell River 0 0 0 0 the Nitinat and McLaughlin Ridge formations and high level intrusions of the Saltspring intrusive 50° Sicker Group . 0 0 suite, as well as abundant gabbroic dikes and sills of the Triassic Mount Hall gabbro. 0 MCLAUGHLIN RIDGE FORMATION: 0 1 1 Major and trace element geochemical data for volcanic rocks of the Big Sicker Mountain area 4 4 1 ç intermediate volcano-sedimentary rocks, 1 indicate a range of rock types spanning basaltic through rhyolitic compositions. Tectonic 4 4 5 QUEEN BEE (L.100G)BELLE (L.55G) felsic volcanic and volcaniclastic rocks, chert 5 discrimination diagrams for the volcanic rocks point to their generation in a volcanic arc setting. Buttle 84 ! 05M-365 and magnetite iron formation Furthermore, light rare earth element (LREE) enrichment, coupled with negative Nb and Ti Lake 30 anomalies, is ubiquitous among the volcanic rocks, suggesting a subduction component in their Buttle Lake Texada NITINAT FORMATION: basalt flows genesis. Island ç U-Pb (zircon) geochronology for felsic volcanic rocks of the McLaughlin Ridge Fm. in the uplift Courtenay 84 NORTHEAST COPPER ZONE southeastern portion of the Cowichan Lake uplift yield ages ranging from 369.1 +/- 6.5 Ma to 339 0 0 0 0 Myra Falls deposit 0 0 0 0 +/- 4.3 Ma, indicating that felsic volcanism of the McLaughlin Ridge Fm. is significantly longer lived 0 05M-368 0 0 0 . than previously thought. 0 80 0 0 0 During the course of this work, numerous altered felsic volcanic rock associated-sulphide 2 2 3 ç 05M-369 3 occurences (unreported in MINFILE) have been indentified up to two kilometres away and Nanoose uplift 1 VICTORIA (L.21G) LENORA (L.35G) 1 4 05M-367 68 4 alongstrike from past producing mines in the Big Sicker Mountain area. Port 5 KEY CITY (L.37G) 5 Alberni ç 05M-36! 3 ç ç 05M-362 81 05M-36661 60 88 Tofino Nanaimo Saltspring 69 ç TYEE (L.36G) RICHARD III (L.39G) ç Introduction 49° Island 0 0 0 ë 0 ë Rocks of the mid-Paleozoic-aged Sicker Group record the development of an oceanic 0 ë 0 0 0 ë 0 ë 0 Bedingfield ë 0 0 ë island arc of enigmatic paleogeography (Yorath et al., 1999), and represent the initial . ë . 0 í 0 uplift Cowichan Lk 0 í 84 0 developmental stages of the Wrangellian superterrane, a fundamental component of the North í 3 82 ë 3 2 í 2 ! American Cordillera. They are also host to the Myra Falls deposit - the largest and most ! 1 ç ç 1 4 í 4 Cowichan Lake í 05M-358 productive volcanogenic massive sulphide (VMS) deposit in western Canada - and numerous ë 5 5 61 í ë 87 ë other past producing VMS mines, VMS occurrences, and other sulphide occurences of uplift ë ë 71 ë ë unresolved metallogeny. ë Mt Sicker and ë Sidney ! ë ë Rocks of the Sicker Group are exposed in four geographically distinct uplifts on Vancouver 05M-364 ë Lara deposits: SYMBOLS ë Island; these are the Buttle Lake, Bedingfield, Nanoose and Cowichan Lake uplifts. However, due ç to a paucity of age control in each of the uplifts, rocks cannot be accurately correlated from one This study Victoria 0 25 50 S1 FOLIATION ë 60 0 ç 0 uplift to the next, and thus, a robust stratigraphy for the Sicker Group as a whole has not been 0 0 0 0 0 ë 0 developed. This has proven to be a significant hamper to the mineral exploration industry, as km 0 0 0 0 Stratigraphic nomenclature for the Sicker and Buttle Lake groups on Vancouver Island. 0 0 workers have traditionally been unable to identify, and subsequently focus their efforts on the S0 BEDDING ë 0 ! LITTLE SICKER 0 most prospective strata of the Sicker Group for VMS mineralization. 4 4 1 1 126° ë 124° 1 ë ë THRUST FAULT MOUNTAIN 1 The proposed Ph.D. research will combine regional and detailed geological mapping with 4 4 geochronological, isotopic, and lithogeochemical studies to better understand the tectonic history 5 ë 5 and metallogeny of the Sicker Group. Geological mapping will establish contact relationships SAMPLES: this study ë between rock formations and establish the geological setting of VMS and potential VMS ë occurrences. Geochronological work will employ U-Pb dating of zircons by laser ablation ICP-MS Distribution of Paleozoic strata of the Sicker and Buttle Lake groups on Vancouver Island and the Gulf Islands. MINFILE OCCURENCES ë ë ë as well as Ar-Ar dating to constrain the ages of major igneous and sedimentary rock units and NEW SULPHIDE OCCURENCE ë develop a detailed chronostratigraphic framework for each of the four structural uplifts. Whole rock lithogeochemistry together with Nd and Hf isotopic studies will be employed to constrain the LIMIT OF MAPPING petrogenesis of the Sicker magmatism and test for any possible involvement with the North American margin in the genesis of Sicker Group magmas. Lead isotopic compositions of 441000.000000 442000.000000 443000.000000 444000.000000 445000.000000 446000.000000 447000.000000 sulphides from various mineral occurrences will be used to discriminate between syngenetic or epigenetic occurrences, in order to help evaluate the potential for additional large VMS deposits in the Sicker Group. Results of the study will enhance our knowledge of Wrangellian tectonic evolution and metallogeny, and lead to a better understanding of a critical part of the history of Preliminary revised geological map for the Mt. Sicker area based on field work conducted for this study. crustal growth in the North American continent. 2006 Field Photos: Geology of the Big Sicker Mountain Area A A A A A A A Geology of the Lenora adit area. Lithological units include A) rhyodacite crystal tuff (?) with abundant malachite staining and pyrite+chalcopyrite stringers up to 10 cm in size; B) variably silica-altered, black graphitic mudstone; and C) strongly sericite+silica-altered tuff (?) with B B B B B B abundant pyrite stringers. Intermediate volcanosedimentary rocks of the Triassic gabbros of the Mount Sicker area: A) Selected new sulphide occurrences: A) 1 to 2% McLaughlin Ridge Formation (?) from the northern hornblende and plagioclase-bearing gabbro; B) pyrite chalcopyrite stringers (up to 15 cm wide) (A) and northeastern (B) parts of the field area. gabbro crosscutting altered and gossanous hosted in quartz-feldspar porphyry, eastern part of volcanosedimentary rocks of the McLaughlin Ridge map area; B) strongly silica+sericite-altered B Formation. volcanosedimentary rock with up to 3% disseminated and stringer pyrite, northeastern part Intermediate to mafic volcanic rocks of of map area. the Nitinat Formation: A) aphyric basaltic andesite with ovoid quartz- epidote patches; B) pyrite-stringer- bearing fault in basaltic andesite flow (?); note hammer for scale in lower central part of photo. C C C Felsic rocks of the McLaughlin Ridge Formation: A) Rocks of the McLaughlin Ridge Formation: A) Structural geology of the Mount Sicker area: A) rhyodacite porphyry, B) heterolithic tuff-breccia, and C) laminated mudstone interbedded with dacitic tuff; east-striking S1 fabric in dacitic tuff is deformed rhyodacite crystal tuff. B) laminated chert; C) magnetite iron formation by F2 kink folds; both of these structures are (approximately 0.5-1 m thick) interbedded with deformed by shallowly plunging F3 folds; B) laminated chert and dacitic to intermediate (?) steeply plunging F1 'M' folds in sericite and silica- tuff. altered rhyodacite tuff; C) north-side-up displacement in fault zone, indicated by drag folding in faulted dacitic tuff. Geochemistry Geochronology Conclusions References 50 Lentz, D. R., 1998, Petrogenetic evolution of felsic volcanic sequences associated The Big Sicker Mountain area is underlain mainly by deformed mafic to felsic volcanic and volcaniclastic rocks of the Nitinat and Phonolite Tholeiitic 390 400 45 600 Ti/V = 10 Ti/V = 20 420 with Phanerozoic volcanic-hosted massive sulfide systems: the role of extensional Transitional Com/Pant McLaughlin Ridge formations and high level intrusions of the Saltspring intrusive suite, as well as abundant gabbroic dikes and sills of the geodynamics: Ore Geology Reviews, v.