GEOLOGICAL SURVEY OF CANADA OPEN FILE 1364. REGIONAL STREAM SEDIMENT AND WATER GEOCHEMICAL RECONNAISSANCE DATA, WESTERN YUKON NTS 115N(E1/2),115O. THE RECONNAISSANCE SURVEY WAS UNDERTAKEN BY THE GEOLOGICAL SURVEY OF CANADA IN CONJUNCTION WITH THE DEPARTMENT OF INDIAN AFFAIRS AND NORTHERN DEVELOPMENT, AND THE GOVERNMENT OF YUKON UNDER THE CANADA-YUKON MINERAL DEVELOPMENT AGREEMENT (1985-1989). E.H.W. HORNBROOK DIRECTED THE SURVEY PROGRAM. P.W.B. FRISKE COORDINATED THE OPERATIONAL ACTIVITIES OF THE CONTRACTING AND GEOLOGICAL SURVEY OF CANADA STAFF THROUGHOUT THE SURVEY. CONTRACTS LET FOR COLLECTION, SAMPLE PREPARATION AND ANALYSIS WERE THE RESPONSIBILITY OF, AND WERE SUPERVISED AND/OR MONITORED BY THE STAFF OF THE EXPLORATION GEOCHEMISTRY SUBDIVISION AS FOLLOWS: COLLECTION: - MONAGHAN DELPH MILLER LTD., DON MILLS, ONTARIO - E.H.W. HORNBROOK, P.W.B FRISKE PREPARATION: - GOLDER ASSOCIATES, OTTAWA, ONTARIO - J.J. LYNCH ANALYSIS: - BONDAR - CLEGG AND COMPANY LTD., OTTAWA - BARRINGER MAGENTA LABORATORIES (ALBERTA) LTD., CALGARY,ALBERTA (WATERS) - CHEMEX LABS LTD.,NORTH VANCOUVER,B.C. (GOLD) - J.J. LYNCH, D.J. ELLWOOD H.R. SCHMITT COORDINATED OPEN FILE PRODUCTION. A.C. GALLETTA MANAGED THE DIGITAL GEOCHEMICAL DATA AND PROVIDED COMPUTER PROCESSING SUPPORT. D.J. ELLWOOD DEVELOPED SOFTWARE TO RASTER PLOT OPEN FILE VALUE,SYMBOL AND REGIONAL TREND MAPS. THE PLOTTING WAS DONE BY CANADA LANDS DATA SYSTEMS STAFF AT ENVIRONMENT CANADA, HULL QUEBEC. M. MCCURDY AND S. COOK PROCESSED INCOMING AND OUTGOING MATERIALS,SUPPLIES AND SAMPLES. COMPUTING,PLOTTING, AND OPEN FILE TEXT LASER PRINTING SERVICES, WERE PROVIDED BY THE COMPUTER SCIENCE CENTER, E.M.R. J. YELLE AND F. WILLIAMS OF THE GEOLOGICAL INFORMATION DIVISION SUPERVISED THE PREPARATION OF OPEN FILE MAPS BY CARTOGRAPHY UNIT A-2. HELICOPTER AND TRUCK SUPPORTED SAMPLE COLLECTION WAS CARRIED OUT DURING THE SUMMER OF 1986. STREAM SEDIMENT AND WATER SAMPLES WERE COLLECTED AT AN AVERAGE DENSITY OF ONE SAMPLE PER 13 SQUARE KILOMETERS THROUGHOUT THE 16600 SQUARE KILOMETERS OF THE WESTERN YUKON SURVEY AREA. SAMPLE SITE DUPLICATE SAMPLES WERE ROUTINELY COLLECTED IN EACH ANALYTICAL BLOCK OF TWENTY SAMPLES. IN OTTAWA, FIELD DRIED SAMPLES WERE AIR-DRIED, SIEVED THROUGH AN 80 MESH SCREEN AND BALL MILLED. THE BALL MILLED FRACTION WAS USED FOR SUBSEQUENT ANALYSES. AT THIS TIME, CONTROL REFERENCE AND BLIND DUPLICATE SAMPLES WERE INSERTED INTO EACH BLOCK OF TWENTY SEDIMENT SAMPLES. FOR THE WATER SAMPLES,ONLY CONTROL REFERENCE SAMPLES WERE INSERTED INTO THE BLOCK. THERE WERE NO BLIND DUPLICATE WATER SAMPLES. ON RECEIPT, FIELD AND ANALYTICAL DATA WERE PROCESSED WITH THE AID OF COMPUTERS. THE FIELD DATA WERE RECORDED BY THE FIELD CONTRACT STAFF ON STANDARD STREAM WATER AND SEDIMENT FIELD CARDS (REV. 74) USED BY THE GEOLOGICAL SURVEY OF CANADA (GARRETT, 1974). THE SAMPLE SITE POSITIONS WERE MARKED ON APPROPRIATE 1/250,000 SCALE NTS MAPS IN THE FIELD. THESE MAPS WERE DIGITIZED AT THE GEOLOGICAL SURVEY IN OTTAWA TO OBTAIN THE SAMPLE SITE UTM COORDINATES. THE SAMPLE SITE COORDINATES WERE CHECKED AS FOLLOWS: A SAMPLE LOCATION MAP WAS PRODUCED ON A CALCOMP 1051 DRUM PLOTTER USING THE DIGITIZED COORDINATES; THE FIELD CONTRACTOR'S SAMPLE LOCATION MAP WAS THEN OVERLAYED WITH THE CALCOMP MAP; THE TWO SETS OF POINTS WERE CHECKED FOR COINCIDENCE. THE DOMINANT ROCK TYPES IN THE STREAM CATCHMENT BASINS WERE IDENTIFIED ON APPROPRIATE GEOLOGICAL MAPS USED AS THE BEDROCK GEOLOGICAL BASE ON RGR MAPS. THOROUGH INSPECTIONS OF THE FIELD AND ANALYTICAL DATA WERE MADE TO CHECK FOR ANY MISSING INFORMATION AND/OR GROSS ERRORS. QUALITY CONTROL AND MONITORING OF THE GEOCHEMICAL DATA WAS UNDERTAKEN BY A STANDARD METHOD USED BY THE EXPLORATION GEOCHEMISTRY SUBDIVISION AT THE GEOLOGICAL SURVEY OF CANADA. FOR THE DETERMINATION OF ZN, CU, PB, NI, CO, AG, MN, FE, CD, AND AS A 1 GRAM SAMPLE WAS REACTED WITH 3 ML CONC. HNO3 IN A TEST TUBE OVERNIGHT AT ROOM TEMPERATURE. AFTER DIGESTION, THE TEST TUBE WAS IMMERSED IN A HOT WATER BATH AT ROOM TEMPERATURE AND BROUGHT UP TO 90C AND HELD AT THIS TEMPERATURE FOR 30 MINUTES WITH PERIODIC SHAKING. 1 ML CONC. HCL WAS ADDED AND HEATING WAS CONTINUED FOR ANOTHER 90 MINUTES. THE SAMPLE SOLUTION WAS THEN DILUTED TO 20 ML WITH METAL FREE WATER AND MIXED. ZN, CU, PB, NI, CO, AG, MN, FE AND CD WERE DETERMINED BY ATOMIC ABSORPTION SPECTROSCOPY USING AN AIR-ACETYLENE FLAME. BACKGROUND CORRECTIONS WERE MADE FOR PB, NI, CO, AG AND CD. AS WAS DETERMINED BY ATOMIC ABSORPTION USING A HYDRIDE EVOLUTION METHOD WHEREIN THE HYDRIDE(ASH3) IS EVOLVED, PASSED THROUGH A HEATED QUARTZ TUBE IN THE LIGHT PATH OF AN ATOMIC ABSORPTION SPECTROPHOTOMETER. THE METHOD IS DESCRIBED BY ASLIN (1976). MOLYBDENUM AND VANADIUM WERE DETERMINED BY ATOMIC ABSORPTION SPECTROSCOPY USING A NITROUS OXIDE ACETYLENE FLAME. A 0.5 GRAM SAMPLE WAS REACTED WITH 1.5 ML CONCENTRATED HN03 AT 90C FOR 30 MINUTES. AT THIS POINT 0.5 ML CONCENTRATED HCL WAS ADDED AND THE DIGESTION WAS CONTINUED AT 90C FOR AN ADDITIONAL 90 MINUTES. AFTER COOLING, 8 ML OF 1250 PPM AL SOLUTION WERE ADDED AND THE SAMPLE SOLUTION WAS DILUTED TO 10 ML BEFORE ASPIRATION. MERCURY WAS DETERMINED BY THE HATCH AND OTT PROCEDURE WITH SOME MODIFICATIONS. THE METHOD IS DESCRIBED BY JONASSON ET AL. (1973). A 0.5 GRAM SAMPLE WAS REACTED WITH 20 ML CONCENTRATED HNO3 AND 1 ML CONCENTRATED HCL IN A TEST-TUBE FOR 10 MINUTES AT ROOM TEMPERATURE PRIOR TO 2 HOURS OF DIGESTION WITH MIXING AT 90C IN A HOT WATER BATH. AFTER DIGESTION, THE SAMPLE SOLUTIONS WERE 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 10% W/V SNSO4 IN M H2SO4. THE HG VAPOUR WAS THEN FLUSHED BY A STREAM OF AIR INTO AN ABSORPTION CELL MOUNTED IN THE LIGHT PATH OF AN ATOMIC ABSORPTION SPECTROPHOTOMETER. ABSORPTION MEASUREMENTS WERE MADE AT 253.7 NM. LOSS ON IGNITION WAS DETERMINED USING A 500 MG SAMPLE. THE SAMPLE, WEIGHED INTO 30 ML BEAKER, WAS PLACED IN A COLD MUFFLE FURNACE AND BROUGHT UP TO 500C OVER A PERIOD OF 2-3 HOURS. THE SAMPLE WAS LEFT AT THIS TEMPERATURE FOR 4 HOURS, THEN ALLOWED TO COOL TO ROOM TEMPERATURE FOR WEIGHING. URANIUM WAS DETERMINED USING A NEUTRON ACTIVATION METHOD WITH DELAYED NEUTRON COUNTING. A DETAILED DESCRIPTION OF THE METHOD IS PROVIDED BY BOULANGER ET AL(1975). IN BRIEF, A 1 GRAM SAMPLE WAS WEIGHED INTO A 7 DRAM POLYETHYLENE VIAL, CAPPED AND SEALED. THE IRRADIATION WAS PROVIDED BY THE SLOWPOKE REACTOR WITH AN OPERATING FLUX OF 5** 10 NEUTRONS/SQ.CM./SEC. THE SAMPLES WERE PNEUMATICALLY TRANSFERRED FROM AN AUTOMATIC LOADER TO THE REACTOR, WHERE EACH SAMPLE WAS IRRADIATED FOR 20 SECONDS. AFTER IRRADIATION, THE SAMPLE WAS AGAIN TRANSFERRED PNEUMATICALLY TO THE COUNTING FACILITY WHERE AFTER A 10 SECOND DELAY THE SAMPLE WAS COUNTED FOR 20 SECONDS WITH SIX HELIUM DETECTOR TUBES EMBEDDED IN PARAFFIN. FOLLOWING COUNTING,THE SAMPLES WERE AUTOMATICALLY EJECTED INTO A SHIELDED STORAGE CONTAINER. CALIBRATION WAS CARRIED OUT ONCE A DAY AS A MINUMUM, USING NATURAL MATERIALS OF KNOWN URANIUM CONCENTRATION. FLUORINE WAS DETERMINED IN STREAM SEDIMENTS AS DESCRIBED BY FICKLIN (1970). A 250 MG SAMPLE WAS SINTERED WITH 1 GRAM OF A FLUX CONSISTING OF TWO PARTS BY WEIGHT SODIUM CARBONATE AND 1 PART BY WEIGHT POTASSIUM NITRATE. THE RESIDUE WAS THEN LEACHED WITH WATER, THE SODIUM CARBONATE WAS NEUTRALIZED WITH 10 ML 10% (W/V) CITRIC ACID AND THE RESULTING SOLUTION WAS DILUTED TO 100 ML WITH WATER. THE PH OF THE RESULTING SOLUTION SHOULD BE FROM 5.5 TO 6.5. THE FLUORIDE CONTENT OF THE TEST SOLUTION WAS THEN MEASURED USING A FLUORIDE ION ELECTRODE. STANDARD SOLUTIONS CONTAIN SODIUM CARBONATE AND CITRIC ACID IN THE SAME QUANTITIES AS THE SAMPLE SOLUTION. A DETECTION LIMIT OF 40 PPM WAS ACHIEVED. GOLD WAS DETERMINED USUALLY ON A 10 GRAM STREAM SEDIMENT SAMPLE; DEPENDING ON THE AMOUNT OF SAMPLE AVAILABLE,LESSER WEIGHTS WERE SOMETIMES USED. THIS RESULTED IN A VARIABLE DETECTION LIMIT:1 PPB FOR A 10 GRAM SAMPLE,2 FOR A 5 GRAM SAMPLE... THE SAMPLE WAS FUSED TO PRODUCE A LEAD BUTTON, COLLECTING ANY GOLD IN THE SAMPLE, WHICH WAS CUPELLED IN A MUFFLE FURNACE TO PRODUCE A SILVER(DORE) BEAD. THE SILVER BEADS WERE IRRADIATED IN A NEUTRON FLUX FOR 1 HOUR,COOLED FOR 4 HOURS,AND COUNTED BY GAMMA RAY SPECTROMETRY.CALIBRATION WAS CARRIED OUT USING STANDARD AND BLANK BEADS. TUNGSTEN WAS DETERMINED AS FOLLOWS: A 0.2 GRAM SAMPLE OF STREAM SEDIMENT WAS FUSED WITH 1 GRAM K2S2O7 IN A RIMLESS TEST TUBE AT 575C FOR 15 MINUTES IN A FURNACE. THE COOLED MELT WAS THEN LEACHED WITH 10 ML CONCENTRATED HCL IN A WATER BATH HEATED TO 85C. AFTER THE SOLUBLE MATERIAL HAD COMPLETELY DISSOLVED, THE INSOLUBLE MATERIAL WAS ALLOWED TO SETTLE AND AN ALIQUOT OF 5 ML WAS TRANSFERRED TO ANOTHER TEST TUBE. 5 ML OF 20% SNCL2 SOLUTION WERE THEN ADDED TO THE SAMPLE ALIQUOT,MIXED AND HEATED FOR 10 MINUTES AT 85C IN A HOT WATER BATH. A 1 ML ALIQUOT OF DITHIOL SOLUTION ( 1% DITHIOL IN ISO-AMYL ACETATE) WAS ADDED TO THE TEST SOLUTION AND THE TEST SOLUTION WAS THEN HEATED FOR 4-6 HOURS AT 80-85C IN A HOT WATER BATH. THE TEST SOLUTION WAS THEN REMOVED FROM THE HOT WATER BATH,COOLED AND 2.5 ML OF KEROSENE ADDED TO DISSOLVE THE GLOBULE. THE COLOUR INTENSITY OF THE KEROSENE SOLUTION WAS MEASURED AT 630 NM USING A SPECTROPHOTOMETER. THE METHOD IS DESCRIBED BY QUIN AND BROOKS (1972). TIN IN STREAM SEDIMENTS WAS DETERMINED AS FOLLOWS:A 200 MG SAMPLE WAS HEATED WITH NH4I;THE SUBLINED SNI4 WAS DISSOLVED IN ACID AND THE TIN DETERMINED BY ATOMIC ABSORPTION SPECTROMETRY. ANTIMONY WAS DETERMINED IN STREAM SEDIMENTS AS DESCRIBED BY (ASLIN,1976). A 500 MG SAMPLE WAS PLACED IN A TEST TUBE; 3 ML CONCENTRATED HNO3 AND 9 ML CONCENTRATED HCL ARE ADDED AND THE MIXTURE WAS ALLOWED TO STAND OVERNIGHT AT ROOM TEMPERATURE.THE MIXTURE WAS HEATED SLOWLY TO 90C AND MAINTAINED AT THIS TEMPERATURE FOR AT LEAST 90 MINUTES. THE SOLUTION WAS COOLED AND DILUTED TO 10 ML. A 400 MICRO L ALIQUOT OF THIS TEST SOLUTION WAS REMOVED AND DILUTED TO 10 ML WITH 1.8M HCL.THE ANTIMONY IN AN ALIQUOT OF THIS DILUTE SOLUTION WAS THEN DETERMINED BY HYDRIDE EVOLUTION-ATOMIC ABSORPTION SPECTROMETRY . BARIUM WAS DETERMINED AS FOLLOWS: A 0.25 GRAM SAMPLE WAS HEATED WITH 5 ML CONC. HF, 5 ML CONC. HCLO4 AND 2 ML CONC. HNO3 TO FUMES OF HCLO4; 3 ML OF CONC. HCLO4 WERE ADDED AND HEATED TO LIGHT FUMES; 5 ML OF WATER WERE ADDED AND THE SOLUTION WAS TRANSFERRED TO A CALIBRATED TEST TUBE AND DILUTED TO 25 ML WITH WATER. BARIUM WAS DETERMINED BY ATOMIC ABSORPTION SPECTROSCOPY USING A NITROUS OXIDE ACETYLENE FLAME. FLUORIDE IN STREAM WATER SAMPLES WAS DETERMINED USING A FLUORIDE ELECTRODE. PRIOR TO MEASUREMENT AN ALIQUOT OF THE SAMPLE WAS MIXED WITH AN EQUAL VOLUME OF TISAB II SOLUTION (TOTAL IONIC STRENGTH ADJUSTMENT BUFFER). THE TISAB II BUFFER SOLUTION WAS PREPARED AS FOLLOWS: 58 GM NACL AND 5 GM CDTA (CYCLOHEXYLENE DINITRILO ACETIC ACID) WERE DISSOLVED IN A MIXTURE OF 50 ML METAL FREE WATER AND 57 ML GLACIAL ACETIC ACID. THE SOLUTION WAS COOLED TO ROOM TEMPERATURE AND THE PH ADJUSTED TO BETWEEN 5.0 AND 5.5 BY NTHE SLOW ADDITION OF 5M NAOH SOLUTION. THE SOLUTION WAS COOLED AND DILUTED TO 1 LITER IN A VOLUMETRIC FLASK. HYDROGEN ION ACTIVITY (PH) WAS MEASURED WITH A COMBINATION GLASS-CALOMEL ELECTRODE AND A PH METER. URANIUM IN WATERS WAS DETERMINED BY A LASER-INDUCED FLUOROMETRIC METHOD USING A SCINTREX UA-3 URANIUM ANALYSER. A COMPLEXING AGENT, KNOWN COMMERCIALLY AS FLURAN AND COMPOSED OF SODIUM PYROPHOSPHATE AND SODIUM MONOPHOSPHATE, (HALL, G.E.M., 1979) WAS ADDED TO PRODUCE THE URANYL PYROPHOSPHATE SPECIES WHICH FLUORESCES WHEN EXPOSED TO THE LASER. SINCE ORGANIC MATTER IN THE SAMPLE CAN CAUSE UNPREDICTABLE BEHAVIOUR, A STANDARD ADDITION METHOD WAS USED. FURTHER, THERE HAVE BEEN INSTANCES AT THE G.S.C. WHERE THE REACTION OF URANIUM WITH FLURAN IS EITHER DELAYED OR SLUGGISH; FOR THIS REASON AN ARBITRARY 24 HOUR TIME DELAY BETWEEN THE ADDITION OF THE FLURAN AND THE ACTUAL READING WAS INCORPORATED INTO THIS METHOD. IN PRACTICE,500 UL OF FLURAN SOLUTION WERE ADDED TO A 5 ML SAMPLE AND ALLOWED TO STAND FOR 24 HOURS. AT THE END OF THIS PERIOD FLUORESCENCE READINGS WERE MADE WITH THE ADDITION OF 0.0, 0.2 AND 0.4 PPB U. FOR HIGH SAMPLES THE ADDITIONS WERE 0.0, 2.0 AND 4.0 (20 UL ALIQUOTS OF EITHER 55 OR 550 PPB U WERE USED). ALL READINGS WERE TAKEN AGAINST A SAMPLE BLANK. REFERENCES ASLIN, G.E.M. (1976) THE DETERMINATION OF ARSENIC AND ANTIMONY IN GEOLOGICAL MATERIALS BY FLAMELESS ATOMIC ABSORPTION SPECTROPHOTOMETER JOURNAL OF GEOCHEMICAL EXPLORATION, VOL. 6,PP. 321-330. BOULANGER, A., EVANS, D.J.R. AND RABY, B.F. (1975) URANIUM ANALYSIS BY NEUTRON ACTIVATION DELAYED NEUTRON COUNTING: PROC. OF THE 7TH ANNUAL SYMP. OF CANADIAN MINERAL ANALYSTS. THUNDER BAY, ONTARIO, SEPT. 22-23, 1975. 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 FLUORIDE IN ROCKS AND SOILS, USING AN ION SELECTIVE ELECTRODE. U.S. GEOL. SURV. PAPER 700C PP. C186-188. GARRETT, R.G. (1974) FIELD DATA AQUISITION METHODS FOR APPLIED GEOCHEMICAL SURVEYS AT THE GEOLOGICAL SURVEY OF CANADA: GEOL SURV. CAN. PAPER 74-52. HALL, G.E.M. (1979) A STUDY OF THE STABILITY OF URANIUM IN WATERS COLLECTED FROM VARIOUS GEOLOGICAL ENVIRONMENTS IN CANADA; IN CURRENT RESEARCH, PART A, GEOL. SURV. CAN. PAPER 79-1A, P. 361-365. HARRIS,J.F. (1982) SAMPLING AND ANALYTICAL REQUIREMENTS FOR EFFECTIVE USE OF GEOCHEMISTRY IN EXPLORATION FOR GOLD. IN LEVINSON,A.A.,EDITOR; PRECIOUS METALS IN THE NORTHERN CORDILLERA, PROCEEDINGS OF A SYMPOSIUM SPONSORED BY THE ASSOCIATION OF EXPLORATION GEOCHEMISTS AND THE CORDILLERAN SECTION OF THE GEOLOGICAL ASSOCIATION OF CANADA,PP.53-67. 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: GEOL. SURV. CAN. PAPER 73-21. QUIN,B.F. AND BROOKS,R.R.(1972) THE RAPID DETERMINATION OF TUNGSTEN IN SOILS, STREAM SEDIMENTS, ROCKS AND VEGETATION. ANAL.CHIM. ACTA. 58 PP 301-309. COMMENTS REGARDING INTERPRETATION OF GOLD RESULTS ------------------------------------------------- THE FOLLOWING DISCUSSION OUTLINES SOME IMPORTANT POINTS TO CONSIDER WHEN INTERPRETING THE GOLD DATA. THIS DISCUSSION IS INCLUDED IN RECOGNITION OF THE SPECIAL GEOCHEMICAL BEHAVIOUR AND MODE OF OCCURRENCE OF AU IN NATURE AND THE RESULTANT DIFFICULTIES IN OBTAINING AND ANALYZING SAMPLES WHICH REFLECT THE ACTUAL CONCENTRATION LEVEL AT A GIVEN SITE. UNDERSTANDING AU GEOCHEMICAL DATA FROM REGIONAL STREAM SEDIMENT OR LAKE SEDIMENT SURVEYS REQUIRES AN APPRECIATION OF THE UNIQUE CHEMICAL AND PHYSICAL CHARACTERISTICS OF AU AND ITS MOBILITY IN THE SURFICIAL ENVIRONMENT. KEY PROPERTIES OF AU THAT DISTINGUISH ITS GEOCHEMICAL BEHAVIOUR FROM MOST OTHER ELEMENTS INCLUDE: 1) AU OCCURS MOST COMMONLY IN THE NATIVE FORM WHICH IS CHEMICALLY AND PHYSICALLY RESISTANT. A HIGH PROPORTION OF THE METAL IS DISPERSED IN MICRON-SIZED PARTICULATE FORM. GOLD'S HIGH SPECIFIC GRAVITY ENSURES HETEROGENEOUS DISTRIBUTION ESPECIALLY IN STREAM SEDIMENT AND CLASTIC-RICH (LOW LOI) LAKE SEDIMENT ENVIRONMENTS. AU DISTRIBUTION APPEARS TO BE MORE HOMOGENEOUS IN ORGANIC-RICH FLUVIATILE AND LAKE SEDIMENT ENVIRONMENTS. 2) AU TYPICALLY OCCURS AT LOW CONCENTRATIONS IN THE PPB RANGE. AU CONCENTRATIONS OF A FEW PPM MAY REPRESENT ECONOMIC DEPOSITS. BACKGROUND LEVELS ENCOUNTERED FOR STREAM AND CENTRE-LAKE SEDIMENTS SELDOM EXCEED 10 PPB, AND COMMONLY ARE NEAR THE DETECTION LIMIT OF 1 PPB. THE MANY FOREGOING FACTORS CAN RESULT IN A PARTICLE SPARSITY EFFECT WHEREIN VERY LOW CONCENTRATIONS OF AU ARE HETEROGENEOUSLY DISTRIBUTED IN THE SURFICIAL ENVIRONMENT. HENCE, A MAJOR PROBLEM FACING THE GEOCHEMIST IS OBTAINING A REPRESENTATIVE SAMPLE. IN GENERAL THE LOWER THE ACTUAL CONCENTRATION OF AU, THE LARGER THE SAMPLE SIZE, OR THE SMALLER THE GRAIN SIZE REQUIRED TO REDUCE UNCERTAINTY OVER WHETHER SUBSAMPLE ANALYTICAL VALUES TRULY REPRESENT ACTUAL VALUES. CONVERSELY, AS ACTUAL AU CONCENTRATIONS INCREASE OR GRAIN SIZE DECREASES, THE NUMBER OF AU PARTICLES TO BE SHARED IN RANDOM SUBSAMPLES INCREASES AND THE VARIABILITY OF RESULTS DECREASES (CLIFTON ET AL., 1969; HARRIS, 1982). THE LIMITED AMOUNT OF MATERIAL COLLECTED DURING THE RAPID, RECONNAISSANCE-STYLE REGIONAL SURVEYS AND THE NEED TO ANALYZE FOR A BROAD SPECTRUM OF ELEMENTS, PRECLUDES THE USE OF A SIGNIFICANTLY LARGE SAMPLE WEIGHT FOR THE AU ANALYSES. THEREFORE, TO THE EXTENT THAT SAMPLE REPRESENTIVITY CAN BE INCREASED, SAMPLE GRAIN SIZE IS REDUCED BY SIEVING AND BALL MILLING OF ALL SAMPLES. IF THE AU IS PRESENT IN A METALLIC STATE, BALL MILLING MAY NOT REDUCE IT'S PARTICLE SIZE SIGNIFICANTLY BECAUSE OF ITS MALLEABILITY. THE FOLLOWING CONTROL METHODS ARE CURRENTLY EMPLOYED TO EVALUATE AND MONITOR THE SAMPLING AND ANALYTICAL VARIABILITY WHICH ARE INHERENT IN THE ANALYSIS OF AU IN GEOCHEMICAL MEDIUMS: 1) FOR EACH BLOCK OF TWENTY SAMPLES: A) RANDOM INSERTION OF A STANDARD REFERENCE SAMPLE TO MONITOR AND CONTROL ANALYTICAL ACCURACY AND LONG-TERM PRECISION, B) COLLECTION OF A FIELD DUPLICATE (TWO SAMPLES SEPARATELY COLLECTED FROM ONE SITE) TO MONITOR SAMPLING VARIANCE, C) ANALYSIS OF A SECOND SUBSAMPLE (BLIND DUPLICATE) FROM ONE SAMPLE TO MONITOR AND CONTROL SHORT-TERM PRECISION; 2) FOR BOTH STREAM SEDIMENTS AND LAKE SEDIMENTS, REPEAT ANALYSES ON A SECOND SUBSAMPLE ARE PERFORMED FOR ALL SAMPLES HAVING VALUES THAT ARE STATISTICALLY ABOVE APPROXIMATELY THE 90TH PERCENTILE OF THE TOTAL DATA SET WITHIN THE SURVEY AREA; 3) FOR LAKE SEDIMENTS ONLY, REPEAT ANALYSIS ON A SECOND SUBSAMPLE WAS PERFORMED ON THOSE SAMPLES WITH LOI VALUES BELOW 10%, INDICATING A LARGE CLASTIC COMPONENT. ON-GOING STUDIES SUGGEST THAT THE AU DISTRIBUTION IN THESE SAMPLES IS MORE LIKELY TO BE HIGHLY VARIABLE THAN IN SAMPLES WITH A HIGHER LOI CONTENT. AU DATA PRESENTATION IS SOMEWHAT DIFFERENT THAN FOR OTHER ELEMENTS. AU DATA INCLUDED IN THIS OPEN FILE IS IN FIVE FIELDS; INITIAL ANALYTICAL RESULTS, REPEAT ANALYTICAL RESULTS, INITIAL SAMPLE WEIGHT, REPEAT SAMPLE WEIGHT AND PLOT STRING. THE FIELD CALLED "PLOT STRING" WAS PLOTTED ON THE VALUE MAPS AND IS CONSTRUCTED AS FOLLOWS. REPEAT ANALYSIS VALUES (NOT FIELD DUPLICATES) ARE PLACED IN BRACKETS FOLLOWING THE INITIAL VALUE DETERMINATION. ALL VALUES DETERMINED ON A SAMPLE LESS THAN 10 G ARE DENOTED BY AN ASTERISK. ACTUAL SAMPLE WEIGHT USED CAN BE DETERMINED FROM THE TEXT. FOLLOWING ARE SOME POSSIBLE VARIATIONS IN THE FORMAT OF THE "PLOT STRING". * NO DATA +27* SINGLE ANALYSIS, <10 G SAMPLE WEIGHT +27(14) REPEAT ANALYSIS, BOTH SAMPLES 10 G +27(14*) REPEAT ANALYSIS, FIRST SAMPLE 10 G, REPEAT <10 G +<1 SINGLE ANALYSIS, 10 G SAMPLE, LESS THAN DETECTION LIMIT OF 1 PPB IN SUMMARY, GEOCHEMICAL FOLLOW-UP INVESTIGATIONS FOR AU SHOULD BE BASED ON A CAREFUL CONSIDERATION OF ALL GEOLOGICAL AND GEOCHEMICAL INFORMATION, AND ESPECIALLY A CAREFUL APPRAISAL OF GOLD GEOCHEMICAL DATA AND ITS VARIABILITY. IN SOME INSTANCES, PROSPECTIVE FOLLOW-UP AREAS MAY BE INDIRECTLY IDENTIFIED BY PATHFINDER ELEMENT ASSOCIATIONS IN FAVOURABLE GEOLOGY, ALTHOUGH A COMPLEMENTARY AU RESPONSE DUE TO NATURAL VARIABILITY MAY BE LACKING. 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. SUBSEQUENT REPEAT SUBSAMPLE ANALYSES WILL INCREASE THE RELIABILITY OF RESULTS AND PERMIT A BETTER UNDERSTANDING OF NATURAL VARIABILITY WHICH CAN THEN BE USED TO IMPROVE SAMPLING METHODOLOGY AND INTERPRETATION. REFERENCES 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. HARRIS,J.F. (1982) SAMPLING AND ANALYTICAL REQUIREMENTS FOR EFFECTIVE USE OF GEOCHEMISTRY IN EXPLORATION FOR GOLD. IN LEVINSON,A.A.,EDITOR; PRECIOUS METALS IN THE NORTHERN CORDILLERA, PROCEEDINGS OF A SYMPOSIUM SPONSORED BY THE ASSOCIATION OF EXPLORATION GEOCHEMISTS AND THE CORDILLERAN SECTION OF THE GEOLOGICAL ASSOCIATION OF CANADA,PP.53-67. ANALYTICAL DATA FORMAT - STREAMS -------------------------------- FIELD MEDIA UNITS RECORD CHARACTERS ZN SEDS PPM 2 16-20 CU SEDS PPM 2 21-25 PB SEDS PPM 2 26-30 NI SEDS PPM 2 31-35 CO SEDS PPM 2 36-40 AG SEDS PPM 2 41-47 MN SEDS PPM 2 48-53 AS SEDS PPM 2 54-60 MO SEDS PPM 2 61-65 FE SEDS PCT 2 66-70 HG SEDS PPB 2 71-75 LOI SEDS PCT 2 76-80 U SEDS PPM 3 16-22 F SEDS PPM 3 23-27 V SEDS PPM 3 28-32 CD SEDS PPM 3 33-39 SB SEDS PPM 3 40-46 W SEDS PPM 3 47-51 BA SEDS PPM 3 52-56 SN SEDS PPM 3 57-61 F WATERS PPB 4 16-20 PH WATERS LOG 4 21-25 U WATERS PPB 4 26-30 INITIAL AU SEDS PPB 4 31-35 REPEAT AU SEDS PPB 4 36-40 INITIAL AU WEIGHT SEDS GRAMS 4 41-44 REPEAT AU WEIGHT SEDS GRAMS 4 45-48 AU PLOT STRING SEDS 4 55-64 NOTE 1: VALUES ARE RECORDED WITH ALL REQUIRED DECIMAL POINTS. THERE ARE NO IMPLIED DECIMAL POINTS. NOTE 2: VALUES LESS THAN A DETECTION LIMIT ARE RECORDED AS A LESS THAN SIGN "<" FOLLOWED BY THE DETECTION LIMIT. NOTE 3: VALUES GREATER THAN AN UPPER LIMIT ARE RECORDED AS A GREATER THAN SIGN ">" FOLLOWED BY THE UPPER LIMIT. NOTE 4: PLEASE SEE GOLD.DOC FOR MORE INFORMATION ON THE AU FIELDS. NOTE 5: PLEASE SEE INTRO.DOC FOR A DESCRIPTION OF ANALYTICAL TECHNIQUES. ROCK MNEMONICS AND AGES FOR OPEN FILE 1364 ------------------------------------------ NOTE: ROCK MNEMONICS MUST ALWAYS BE USED IN CONJUNCTION WITH AGE AS THE MNEMONIC MAY BE REPEATED. ROCK AGE DESCRIPTION ---- --- ----------- QUATERNARY RECENT SELKIRK GROUP RS 64 BASALT,ANDESITE FLOWS,BRECCIA,TUFF. PLEISTOCENE AND RECENT QS 64 GLACIAL AND SURFICIAL DEPOSITS. TERTIARY OLIGOCENE AND MIOCENE OMCV 61 ANDESITE,BASALT,BRECCIA. OMD 61 DONJEK:TUFF,BRECCIA. OLIGOCENE CARMACKS GROUP OCS 60 CONGLOMERATE,SANDSTONE,SHALE. LOWER TERTIARY ITS 58 CONGLOMERATE,SANDSTONE,SHALE. TVR 58 RHYOLITE,QUARTZ FELDSPAR PORPHYRY. EARLY TERTIARY ETF 57 GRANITE AND SYENITE PORPHYRY, RHYOLITE. CRETACEOUS KY 52 SYENITE,MONZONITE. KQM 52 QUARTZ MONZONITE,GRANODIORITE;CASSIAR QUARTZ MONZONITE,ALASKITE. TRIASSIC TGDN 42 FOLIATED HORNBLENDE GRANODIORITE, QUARTZ. PALEOZOIC AND MESOZOIC UNDIVIDED PMUB 40 ULTRAMAFIC ROCKS PALEOZOIC UNDIVIDED PN 09 NASINA:GRAPHITIC QUARTZITE,SCHIST. PC 09 LIMESTONE. PTV 09 CHERT,VOLCANIC ROCKS,SLATE. PV 09 GREENSTONE,AMPHIBOLITE. PQMN 09 FOLIATED MUSCOVITE QUARTZ MONZONITE. PGDN 09 PELLY GNEISS:FOLIATED TO GNEISSIC GRANODIORITE. PERMIAN SKOLAI GROUP PS 36 ANDESITE,BASALT,ULTRAMAFICS,PYROCLASTICS, PHYLLITE,CHERT,LIMESTONE,CONGLOMERATE. CARBONIFEROUS AND PERMIAN CPS 35 QUARTZ-MUSCOVITE SCHIST. CPSN 35 SCHIST,GNEISS,INCLUDES BIG SALMON METAMORPHIC COMPLEX. CPUB 35 SERPENTITE,DIORITE,PYROXENITE, PERIDOTITE.