MINISTRY OF ENERGY, MINES AND PETROLEUM RESOURCES Mineral Resources Division Geological Survey Branch Environmental Geology Section File : 104M.DOC Date : August 4, 1993 REGIONAL GEOCHEMICAL SURVEY - DIGITAL DATA BC RGS 37 - NTS 104M Skagway ... INTRODUCTION Open File BC RGS 37 was published on August 4, 1993 as part of the British Columbia Regional Geochemical Survey (RGS) Program. This Open File DISKETTE includes analytical and field data compiled from a reconnaissance scale stream-sediment and water survey conducted in NTS map sheet 104M - Skagway during the 1992 field season. Adjacent NTS map sheets 1140 - Yakutat and 114P - Tatshenshini were also surveyed as part of the 1992 RGS field program. The 1992 surveys and production of Open File BC RGS 37 were managed by the British Columbia Ministry of Energy, Mines and Petroleum Resources (MEMPR) and are a contribution to the Corporate Resource Inventory Initiative (CRII). Analytical data and field observations compiled by the RGS Program are used in the development of a high quality geochemical database suitable for resource assessment, mineral exploration, geological mapping and environmental studies. Sample collection, preparation and analysis are closely monitored by the MEMPR to ensure consistency and conformance to national standards. ACKNOWLEDGMENTS The RGS Program is managed by Geological Survey Branch staff of the MEMPR. P.F. Matysek and W. Jackaman coordinated the operational activities of contract and MEMPR staff. W. Jackaman monitored the field program and produced this Open File. COLLECTION : McElhanney Engineering Services Ltd., Surrey, B.C. PREPARATION : Rossbacher Laboratories Ltd., Burnaby, B.C. ANALYSIS : Barringer Laboratories Ltd., Calgary, Alta. (sediments) Activation Laboratories Ltd., Ancaster, Ont. (INAA - sediments) Chemex Laboratories Ltd., North Vancouver, B.C. (waters) SURVEY DETAILS Physiography and Geology Situated in the northwest corner of British Columbia, NTS map sheet 104M - Skagway includes the Coast Mountain and Tagish Highland physiographic subdivisions (Holland, 1976). Trending southeast to northwest, the Coast Mountains extend along the western portion of the map sheet and are characterized by rugged mountain peaks separated by numerous glaciers and snowfields. Bordering the Coast Mountains to the northeast is a transition zone (Tagish Highlands) between the Coast Mountains and the Yukon Plateaus. The Tagish Highlands contains relatively smooth and gently sloping mountains separated by wide, U-shaped valleys. The survey area presently contains 87 recorded mineral occurrences and is best known for the Gridiron, Ben-My-Chree and Engineer gold-silver past producers. Underlain by the Intermontane and Coast Crystalline tectonic belts, potential exploration targets include precious metal vein deposits, gold-quartz veins, gold- stibnite veins, auriferous quartz-carbonate zones and gold rich skarns. The bedrock geology base map used in Open File BC RGS 37 is modified from an unpublished compilation by Mihalynuk and Smith, 1993 (Table 1). Table 1. Bedrock Geology Legend - NTS 104M QUATERNARY DEPOSITS Qal Extensive areas of unconsolidated glacial till and poorly sorted alluvium. INTRUSIVE ROCKS eTg,eTgd Coast plutonic complex, dominantly granodiorite and other undifferentiated granitoids. KTg Late Cretaceous to Eocene granitoid rocks of the Coast Mountains, undifferentiated. lKg,lKgd Late Cretaceous undifferentiated granitoid rocks; granodiorite. Mainly associated with the Coast plutonic complex. Kg,Kqm Undifferentiated Cretaceous granitoid rocks. In part equivalent to lKg. eKg, eKt Early Cretaceous undifferentiated granitoid rocks; tonalite. mlJg Middle or late Jurassic granotoids. eJgd,eJh Hale Mountain granodiorite and related(?) hornblendite (184-187 Ma). lTgd,lTg Granodiorite, minor leucogranite, quartz lThg diorite, and gabbro of late Triassic age. May be altered or slightly deformed. Includes the Bennett pluton. PTgd Permo-Triassic(?) intrusive rocks of unknown affinity. LATE MESOZOIC/TERTIARY EXTRUSIVE ASSEMBLAGES Es Skukum volcanic suite; mainly intra-caldera facies dominated by intermediate to felsic tuffs and flows of Eocene age. eEs Sloko Group, undivided, aerially extensive rhyolite to andesite breccia and tuff of Early Eocene age. Pt Tagish volcanic suite; dominantly intra- caldera megabreccia and intermediate to felsic tuffs and flows of Paleocene age. Km Montana Mountain suite. Mainly intermediate to felsic tuffs and flows. lKtv Windy-Table volcanic suite. Quartz-phyric ash flows and intermediate breccia and tuff. lmJv Tutshi volcanic suite. Basalt to dacite flows and tuff of interpreted lower to middle Jurassic age. lJL Laberge Group undifferentiated. Includes siltstone, arenaceous greywacke, argillite, and conglomerate of Early Jurassic age. lJLg Laberge Group; mainly medium to coarse, quartz-bearing wacke. lJLa Laberge Group; mainly argillite with subordinate siltstone and wacke. OLDER VOLCANIC ASSEMBLAGES, SEDIMENTARY, AND METAMORPHIC ROCKS STIKINE(?) TERRANE uTs Stuhini Group, undifferentiated. Includes feldspar-phyric and pyroxene-phyric flows, tuff, tuffite, and breccia; conglomerate, limestone, argillite. uTss Stuhini Group; dominated by volcanic derived sediments of coarse conglomerate to silty argillite composition. uTsv Stuhini Group; dominated by bladed plagioclase and pyroxene-phyric flows rocks (lower) or intermediate tuffs (higher in section). PPmb Boundary Ranges metamorphic suite, undifferentiated: Metamorphosed siltstone, greywacke, tuff, greenstone, and limestone metamorphosed to transitional greenschist- amphibolite facies, regionally retrograded. Current data permits a Permian to Devonian age. CACHE CREEK TERRANE MTc Undifferentiated Cache Creek Complex. Sheared melange consisting of pods of ultramafic rocks, greenstone, marble, chert, and clastics in a sheared matrix of greywacke and argillite. Mississippian to Late Triassic age. MTCs Mainly pelagic and hemipelagic sediments MTCl Mainly limestone MTCb Pillow basalt, gabbro and minor ultramafic tectonite. TP Undivided Peninsula Mountain volcano- sedimentary suite. Includes basaltic to rhyolitic tuff, breccia and tuff of Middle to Late Triassic age. NISLING TERRANE? PPgn Florence Range Metamorphic Suite. Includes semipelitic, pelitic, carbonate, amphibolite and calcsilicate schist and gneiss. Paleozoic and Late Proterozoic protoliths are most likely. PMgn Gneiss and schist; age and affinity uncertain, but possibly Mezozoic or older. Sample Collection Helicopter and truck-supported sample collection was carried out during July and August of 1992. A total of 785 stream sediment and 773 stream water samples were systematically collected from 741 sites. Average sample site density was 1 site per 10 square kilometres over the 7500 square kilometre survey area. One field duplicate sample was routinely collected in each analytical block of twenty samples. The survey also included the collection of 43 sediment and water samples in Atlin Provincial Park and Recreation Area. The majority of primary and secondary drainage basins having catchment areas of less than 10 square kilometres were sampled. At each site sediment samples weighing 1 to 2 kilograms were collected within the active (subject to annual flooding) stream channel and placed in kraft-bags. Samples were primarily composed of fine-grained material mixed with varying amounts of coarse sand and gravel, glacial sediments and organic material. Contaminated or poor-quality sample sites were avoided by choosing an alternate stream or by sampling a minimum of 60 metres upstream from the identified source of contamination. In order to minimize the glacial flour component of samples collected from glacial streams, the coarser grained material below the surface layer was sampled. Unfiltered water samples free of suspended material were collected in 250-millilitre bottles. Field observations regarding sample media, sample site and local terrain were also recorded. To assist follow-up, aluminum tags inscribed with a RGS sample site identification number (ie. 921002) were fixed to permanent objects, when available, at each site. Recorded field observations (Appendix A) indicate that 14 per cent of the sample sites are located in the Coast Mountains (youthful mountains). Creeks found in this area tend to be fast flowing and are often charged with sediments from melting ice. A total of 311 sites list glacial melt water as the stream water source. Over 80 per cent of the sample sites are located within areas characterized by mature mountains (Tagish Highlands). This region contains creeks which tend to be slower flowing and produce sediment material with a slightly higher organic composition. Sediment samples collected in the Tagish Highland average 6.1 per cent loss on ignition and only 3.3 per cent loss on ignition for samples collected in areas listed as youthful mountains. The overall stream width and depth at each sample site average 5.0 metres and 85 centimetres respectively. Sample Preparation At a field camp established in Atlin, sediment samples were air- dried at a temperature range of 30ĄC to less than 50ĄC and material finer than 1 mm was recovered by sieving each sample through a -18 mesh ASTM screen. Samples were shipped to Rossbacher Laboratories Ltd. (Burnaby, B.C.) for final processing. The -80 mesh (<177 microns) fraction was obtained for analyses by dry sieving each sample. Quality control reference standards and analytical duplicate samples were inserted into each analytical block of twenty sediment samples. A quantity of -80 mesh material and a representative sample of the +80 to -18 mesh fraction was archived for future studies. Control reference water standards were inserted into each analytical block of 20 water samples. Sample Analysis - Routine Analytical Suite Barringer Laboratories Ltd. (Calgary, Alta.) analyzed the sediment samples for antimony, arsenic, bismuth, cadmium, cobalt, copper, fluorine, iron, lead, manganese, mercury, molybdenum, nickel, silver, vanadium, zinc and loss on ignition. Water samples were analyzed for fluoride, uranium, sulphate and pH by Chemex Laboratories Ltd. (North Vancouver, B.C.). Laboratory reported detection limits for each element are listed in Table 2. Table 2. RGS suite of elements: NTS 104M Detection Detection Element Limit Method Element Limit Method Antimony 0.2 ppm AAS Gold 2 ppb INAA Arsenic 0.2 ppm AAS-H Antimony 0.1 ppm INAA Bismuth 0.2 ppm AAS-H Arsenic 0.5 ppm INAA Cadmium 0.2 ppm AAS Barium 50 ppm INAA Cobalt 2 ppm AAS Bromine 0.5 ppm INAA Copper 2 ppm AAS Cerium 3 ppm INAA Fluorine 40 ppm ION Cesium 1 ppm INAA Iron 0.02 % AAS Chromium 5 ppm INAA Lead 2 ppm AAS Cobalt 1 ppm INAA Manganese 5 ppm AAS Hafnium 1 ppm INAA Mercury 10 ppb AAS-F Iron 0.02 % INAA Molybdenum 1 ppm AAS Lanthanum 1 ppm INAA Nickel 2 ppm AAS Lutetium 0.05 ppm INAA Silver 0.2 ppm AAS Molybdenum 1 ppm INAA Vanadium 5 ppm AAS Nickel 20 ppm INAA Zinc 2 ppm AAS Rubidium 15 ppm INAA LOI 1.0 % GRAV Samarium 0.1 ppm INAA Scandium 0.1 ppm INAA Fluoride 20 ppb ION Sodium 0.01 % INAA Uranium 0.05ppb LIF Tantalum 0.5 ppm INAA Sulphate 1 ppm TURB Terbium 0.5 ppm INAA pH 0.1 GCE Thorium 0.5 ppm INAA Tungsten 1 ppm INAA Uranium 0.5 ppm INAA Ytterbium 0.2 ppm INAA Antimony was determined as described by Aslin (1976). A 0.5 gram sample was placed in a test tube with 3 ml concentrated HNO3 and 9 ml HCl. The mixture was allowed to stand overnight at room temperature prior to being heated to 90ĄC and maintained at this temperature for 90 minutes. The mixture was cooled and a 1 ml aliquot was diluted to 10 ml with 1.8M HCl. This dilute solution was determined by hydride evolution-atomic absorption spectroscopy (AAS). Arsenic and bismuth were determined on a 1 gram sample reacted with 3 ml of concentrated HNO3 for 30 minutes at 90ĄC. Concentrated HCl (1 ml) was added and the digestion was continued at 90ĄC for an additional 90 minutes. A 1 ml aliquot was diluted to 10 ml with 1.5M HCl in a clean test tube. The diluted sample solution was added to a sodium borohydride solution and aspirated through a heated quartz tube in the light path of an atomic absorption spectrometer (AAS-H). For the determination of cadmium, cobalt, copper, iron, lead, manganese, nickel, silver, and zinc, a 1 gram sample was reacted with 3 ml of concentrated HNO3 for 30 minutes at 90ĄC. Concentrated HCl (1 ml) was added and the digestion was continued at 90ĄC for an additional 90 minutes. The sample solution was then diluted to 20 ml with metal free water and mixed. Concentrations were determined by AAS using an air-acetylene flame. Background corrections were made for Pb, Ni, Co and Ag. Fluorine was determined as described in Ficklin (1970). A 0.25 gram sample was sintered with a 1 gram flux consisting of 2 parts by weight Na2CO3 and 1 part by weight KNO3. The residue was then leached with water and the Na2CO3 was neutralized with 10 ml 10% (w/v) citric acid. The resulting solution was diluted to 100 ml with water to a pH of 5.5 to 6.5 and measured using a fluoride ion electrode (ION). Mercury was determined using a 0.5 gram sample reacted with 20 ml concentrated HNO3 and 1 ml concentrated HCl in a test tube for 10 minutes at room temperature and for 2 hours in a 90ĄC water bath. After digestion the sample was cooled and diluted to 100 ml with metal free water. The Hg present was reduced to the elemental state by the addition of 10 ml of 10% w/v SnSO4 in H2SO4. The Hg vapor was flushed by a stream of air into an absorption cell mounted in the light path of an atomic absorption spectrometer (AAS-F). Measurements were made at 253.7 nm. This method is described by Jonasson, et al. (1973). Molybdenum and vanadium were determined by AAS using nitrous oxide acetylene flame. A 0.5 gram sample was reacted with 1.5 ml concentrated HNO3 at 90ĄC for 30 minutes. At this point 0.5 ml of concentrated HCl was added and the digestion continued for an additional 90 minutes. After cooling, 8 ml of 1250 ppm Al solution was added and the sample solution diluted to 10 ml before aspiration by AAS. Loss on ignition was determined using a 0.5 gram sample. The sample was weighed into a 30 ml beaker, placed in a cold muffle furnace and heated to 500ĄC over a period of 2 to 3 hours. The sample was left at this temperature for 4 hours, then cooled to room temperature before weighing (GRAV). Fluoride in waters was determined using a specific ion electrode. An aliquot of sample was mixed with an equal volume of total ionic strength adjustment buffer (TISAB II solution). The fluoride was measured using a Corning 101 Electrometer with an Orion Fluoride Electrode (ION). Uranium in waters was determined by a fluorometric method. The U was initially preconcentrated by evaporation. The residue was fused with a mixture of Na2CO3, K2CO3 and NaF in a platinum dish. After cooling the fluorescence of the fused pellet was measured using a Turner Fluorometer (LIF). Sulphate in waters was determined on 50 ml sample mixed with 0.3 ml of Sulfaver IV reagent. The solution is poured into a spectrometer absorption cell and the turbidity is measured at 420 nm (TURB). pH in waters was measured using an aliquot of sample in a clean dry beaker by a Fisher Accumet pH Meter (GCE). Sample Analysis - INAA The determination of gold, antimony, arsenic, barium, bromine, cerium, cesium, chromium, cobalt, hafnium, iron, lanthanum, lutetium, molybdenum, nickel, rubidium, samarium, scandium, sodium, tantalum, terbium, thorium, tungsten, uranium and ytterbium by INAA was conducted by Activation Laboratories Ltd. (Ancaster, Ont.). This analytical technique involves irradiating the sediment samples, which on average weigh 15 grams, for 20 minutes in a neutron flux of 1011 neutrons/cm2/second. After a decay period of approximately 1 week, gamma-ray emissions for the elements were measured using a gamma-ray spectrometer with a high resolution, coaxial germanium detector. Counting time was approximately 15 minutes per sample and the results were compiled on a computer and later converted to concentrations. Table 2 lists the associated laboratory reported detection limits for this analytical technique. Repeat analysis by INAA have also been performed on a separate split for samples reporting gold values exceeding 23 ppb and are listed as Au2 in Appendix A.. This level represents the 95th percentile for gold based on the total 1992 analytical data set (NTS map sheets 104M, 114O and 114P). INTERPRETATION OF GOLD DATA Understanding gold geochemical data from regional stream sediment surveys requires an understanding of the chemical and physical characteristics of gold in the surficial environment. Gold is a soft, malleable element of high density (19.3 g/cm3). Gold is chemically inert and commonly occurs in native form (pure Au) or as electrum (alloyed with silver). Sub-micron sized gold is often bound to clays, adsorbed onto Fe-Mn oxides or contained within organic colloids. At normal surface temperatures, gold will dissolve under rare conditions of high oxidation potential and high acidity where ions such as chloride (Cl-), thiosulphate (S2O3-2) or cyanide (CN-) are present. Normal background concentrations for gold in bedrock vary, but are generally less than 5 ppb. Background levels encountered for stream sediments seldom exceed 10 ppb and commonly are near the detection limit of 2 ppb. Gold generally occurs as rare, discrete particles. In many instances a geochemical subsample may or may not contain a gold grain. This is known as the 'nugget effect'. Generally, larger geochemical sample sizes are required to minimize the nugget effect and more accurately represent gold concentrations. (Clifton et al., 1969; Harris, 1982). Neutron activation analyses for the 1992 RGS analytical program utilized samples weighing on average 15 grams. Follow-up investigations of gold anomalies should be based on careful consideration of related geological and geochemical information and an understanding of the variability of gold geochemical data. Once an anomalous area has been identified, field investigations should be designed to include detailed geochemical follow-up surveys and collection of large, representative samples. Analysis of field and analytical duplicate samples enables assessment of the reliability of gold results and permits better data interpretation. REFERENCES Aslin, G.E.M. (1976): The Determination of Arsenic and Antimony in Geological Materials by Flameless Atomic Absorption Spectrophotometry; Journal of Geochemical Exploration, Volume 6, pp. 321-330. Clifton, H.E., Hunter, R.E., Swanson, F.J. and Phillips, R.L. (1969): Sample Size and Meaningful Gold Analysis; U.S. Geological Survey, Professional Paper, 625-C. Ficklin, W.H. (1970): A Rapid Method for the Determination of Fluorine in Rocks and Soils, Using an Ion Selective Electrode; U.S. Geological Survey, Paper 700C, pp. C186-188. Harris, J.F. (1982): Sampling and Analytical Requirements for Effective use of Geochemistry in Exploration for Gold; Precious Metals in the Northern Cordillera; in Symposium proceedings, A.A., Levinson, Editor; Association of Exploration Geochemists and Geological Association of Canada, Cordilleran Section, pp. 53-67. Holland, S.S. (1976): Landforms of British Columbia, A Physiographic Outline; B.C. Ministry of Energy, Mines and Petroleum Resources, Bulletin 48. Jonasson, I.R., Lynch, J.J. and Trip, L.J. (1973) Field and Laboratory Methods used by the Geological Survey of Canada in Geochemical Surveys: No. 12, Mercury in Ores, Rocks, Soils, Sediments and Water; Geological Survey of Canada, Paper 73- 21. Mihalynuk, M. and Smith, M. (1993): Geology compilation of map sheet 104M - Skagway (unpublished). Plant, J. (1971): Orientation Studies on Stream Sediment Sampling for a Regional Geochemical Survey in Northern Scotland, Institute of Mining and Metallurgy, Transactions, Volume 80, pp. B324-345.