Toodoggone Geoscience Partnership: Preliminary Bedrock Mapping Results from the Swannell Range: Finlay River – Toodoggone River Area (NTS 94E/2 and 7), North-Central British Columbia1 By L. Diakow, G. Nixon, B. Lane and R. Rhodes KEYWORDS: P3, public-private partnership, Targeted Toodoggone River in the north and east (Fig. 1). The new Geoscience Initiative II (TGI-II), bedrock mapping, result s reporte d below em phasiz e changes in the Early Ju- stratigraphy, Finlay River, Toodoggone River airborne ras sic stra tig ra phy of the Toodoggone from west to east. gamma-ray spectrometric and magnetic survey, Toodoggone River, Finlay River, Toodoggone formation, Black Lake Intrusive Suite, Cu-Au porphyry, epithermal LITHOSTRATIGRAPHIC UNITS Au-Ag Over the past two field seasons, nearly 600 km2 of the INTRODUCTION Swannell Ranges, situ ated be tween the major drainages of the Toodoggone and Finlay rivers and their conflu ence , The Toodoggone Geoscience Part ner ship was ini tiated have been mapped in detai l, thereby refin ing Juras sic stra - in 2003 to gener ate detai led geoscience infor m ati on, in- tig raphy that was, for the most part, pre viously assigne d to clud ing air borne geo phys ics and bed rock ge ol ogy maps, an un di vided Hazelton Group map unit (Diakow et al., that would sup port min ing ex plo ra tion in pre vi ously ex- 1985, 1993). As a conse quence of mapping in 2004, a re - plored and more re mote ter rain in the east-cen tral gion of pre viously un divided Ju rassic rocks is now iden ti - Toodoggone River and McConnell Creek map ar eas, which fied as part of the Toodoggone form ati on. These rocks have are con sidered highly prospec tive for Cu-Au porphyry and been sub di vided in for mally into strati graphic mem bers, epi ther mal Au-Ag min er al iza tion. The suc cess of this part - which collec tively repre sent one of the most com plete nership is based on the parti ci pa ti on of all five mining com - Early Ju ras sic se quences ex posed any where in the panies acti vely explor ing the program area (Stealth Min er- Toodoggone River area. Vol ca nic rocks pre sumed to be als Ltd., Northgate Min er als Corp., Finlay Min er als Ltd., near the bottom of the Toodoggone form ati on rest un con- Bishop Gold Inc. and Sa ble Resource s Ltd.), coupled with form ably on ei ther volca nic strata of the Late Tri as sic Takla per son nel from the British Co lum bia Geo log i cal Sur vey, Group or granitoid rocks of the Early Juras sic Black Lake the Geological Survey of Canada and the University of Intru sive Suite. The oldest rocks con sist of bed ded sed i- British Columbia. men tary strata of the Up per Pa leo zoic Asitka Group; these In 2004, the Geolog i cal Survey of Can ada re leased are gen erall y poorly ex posed, lo cally intrude d and ther- digi tal data and a serie s of maps from a low-level, high-res- mally al tered by Juras sic intru sions , and rarely observe d to o lu tion air borne gamma-ray spec tro met ric and mag netic be overlai n disconformably by the Takla Group. survey that cov ered 1) most of the known porphyry and epi - The gen eral ize d geol ogy of the study area is shown in ther mal tar gets within the main area of pro spec tive Early Fig ures 2 and 3, and repre sen ta ti ve stratigraphi c secti ons Juras sic rocks; and 2) a re mote and rel ati vely under- are given in Fig ure 4. The stra tig raphy is transected by ma- explored region farther east in the Swannell Ranges of the jor northerl y to north-north west erly-trending high-an gle Toodoggone area (Shives et al., 2004). faults, no ta bly the Pil lar and Black faults, in ter sected by Bed rock map ping con tin ued in 2004, ex pand ing the easterl y to northeas terl y-trending cross-faults (Fig. 2). East area of detai led 1:20 000-scale map cover age in two re - of the Pil lar Fault, the stra tig ra phy is con sis tently in clined gions: 1) the southern region, lo cated 55 km southeas t of to the west-south west and has rel ati vely shal low dips (15– the Kemess South Cu-Au porphyry mine and cen tred on 25°). Johanson Lake (Schiarizza, 2004a, b; Schiarizza and Tan, this volum e); and 2) the northern region, be tween the Asitka Group (Unit PAs) Toodoggone and Finlay rivers (Diakow, 2004). This paper sum ma rizes the re sults of geo log i cal map ping con ducted in The Penn syl vanian to Early Perm ian Asitka Group a 250 km2 area lo cated east of the Pillar Fault (Diakow, com prises several large pendants rest ing on or ad jacent to 2004) and bounded by the Finlay River in the south and the the Early Juras sic Duncan pluton near Drybrough Peak (west of the study area), where both vol canic and stratigraphically higher sed im en tary rocks were mapped 1Contribution of the Federal-Provincial Targeted Geoscience pre vi ously (Diakow, 2004). In this study, scatter ed out- Initiative-II (TGI-II) crops of the Asitka Group were encoun ter ed near the Geo log i cal Field work 2004, Pa per 2005-1 93 u k a c h i d a C h R Study ' º 0 7 5 2 º 1 57°30’ N E R 6 2 Area O N 1 T o n e R O D O G G o d o g g o T O Baker M o u n t G r a v e s Pine R y a Kemess l S Sophia n A i M F U E L Sickle-Griz 94E B 57°00’ N L 94D Pil North A C Alexandra 57º20' K R A N G k E e ' e 0 4 r º 6 C 2 1 T h e P i l l a r R t k u t c s W o u ’ S 0 J 0 ° 7 2 1 Pil South W ’ R Airborne Magnetic-Radiometric Survey 0 Brenda 0 57º15' ° Shives et al., 2004 6 Y 2 1 A Bedrock Mapping Studies L N I Pine 2005 proposed mapping F Diakow et al., this study Diakow, 2004 Diakow, 2001 Diakow et al., 1993 and 1985 1:20000 Mapping 0 2 4 Schiarizza, 2004 and Schiarizza and Tan, this volume Active Mining Properties kilometers Legun, 2001 MINFILE Occurrence Monger, 1977 Eisbacher, 1974 Provincial Park Fig ure 1. Lo ca tion of bed rock map ping com pleted in 2004. In set on the left shows published geo log i cal work in the Toodoggone River (94E) and McConnell Creek (94D) map ar eas (see ref er ences). treeline in an area east of Jock Creek (Fig. 2). Here, the suc - phyric ba salt flow that over lies siltstones consid ered to rep- ces sion is about 130 m thick and in truded by an Early Juras - resent part of the un derly ing Asitka Group. This contac t is sic quartz monzonite stock at the lower contac t. Limestone in ter preted as a disconformity, al though there is lit tle ev i - ad ja cent to the in tru sive con tact is recrystallized and re - dence of erosion. Above this con tact, lavas more typi cal of placed lo cally by ir reg u lar zones of di op side-gar net-mag- the Takla Group predom inate , and in clude a vari ety of por- ne tite skarn, and car ries patchy ga lena and chalco py rite phy ritic bas alts contai n ing abundant, medium to coarse min er aliza tion. Higher in the sec tion, pale grey weath ered (<6 mm) pheno crysts of clinopyroxene. Other, volu metri - limeston e al ter nates with whit ish chert in beds vary ing cally mi nor flow va ri et ies in clude dis tinc tive por phy ritic from 10 to 50 cm thick. Above the highest chert lay ers, lavas with bladed-plagioclase texture s and aphani ti c bas- siltstone inter leaved with thin black mudstone part ings oc - alts. Pyroxene-bearing sand stones occur as sparse, thin cupies the upper m ost 20 m of the sec tion. The upper m ost interbeds within the volcanic succession. sedi m entar y strata are sharply overlain by pyroxene- bearing lavas of the Late Triassic Takla Group. Basal Toodoggone Formation Unconformity Takla Group (Unit uTTv) Bed ded polymictic con glom er ates and sand stones The Late Tri as sic Takla Group is ex posed along the (unit Tc1) occur at a num ber of isolat ed local iti es in the lower north- and east-facing slopes of the moun tains south south ern Toodoggone map area, and oc cupy the in ter val of Jock Creek, and in nearby outcrops where it is juxta - be tween mafic vol ca nic rocks of the Takla Group and over- posed against the Toodoggone form ati on by high-angle ly ing quartz-bi o tite-bear ing vol ca nic rocks of the faults.