Slide 1: Why understanding placer gold is important for lode exploration in the Klondike
Why understanding placer gold is i important t t for f lode l d exploration l ti iin the Klondike Rob ob C Chapman ap a (Placer Minerals Group, University of Leeds, UK) Jim Mortensen (UBC Vancouver)
Slide 2: The Klondike Gold Rush
TheKlondikeGoldRush PlacergoldwasdiscoveredonRabbitCreek(promptlyre Placer gold as disco ered on Rabbit Creek (promptl re namedBonanzaCreek)onAugust16,1896 Bonanza(Rabbit)Creekinfallof1896
Slide 3: At least 16 million ounces of gold likely produced
Itislikelythatatleast16millionounces(~500tonnes)and possiblyasmuchas20millionounces(~650tonnes)ofgoldwas actually produced actuallyproduced Thiswasfromadistrictthatwasonly~50kmby~30km(1500 km2)inarea ) TheKlondiketrulywas(is?)oneofthegreatplacergoldmining districtsintheworld
Slide 4: Where did the gold come from?
Gold-bearing quartz veins were discovered in the Klondike within a year of the first discovery of placer gold But…..there But there were 400 tonnes (possibly as much as 650 tonnes) of placer gold recovered from the Klondike but < 40 kg of lode gold…… The obvious question is: Where did the gold come
Slide 5: Gold in the Klondike
Gold in the Klondike….. GoldintheKlondike….. • Thereareatleastninedistinctstylesoflode There are at least nine distinct styles of lode mineralization intheKlondike • ButonlythequartzveinswithintheKlondike Schistareknowntoactuallycontain significantamountsofgold– allotherstyles ofmineralizationappear
Slide 6: Where can we find gold in rocks?
Where can we find gold in rocks? Not all quartz veins contain gold! This doesn’t (quartz formed during metamorphism) But this does: Discordant sco da t veins e s with t pyritic selvage
Slide 7: The story in the placer gold
The story in the placer gold The Klondike is famous for the Gold rush of 1896 and mining continues But the placer gold itself may provide a key to finding the source
Slide 8: Lone Star: How the chemistry of gold can help
Lone Star: How the chemistry of gold can help….. Populations of gold grains from lodes (stars) and placers (points) were analysed Composition p varied systematically away from Lone Star Broadly B dl concentric ti compositional zones were identified centring identified, Whatdoesthismean? on Lone Star
Slide 9: Gold composition and the source of the Eldorado Creek Gold
Gold composition and the source of the Eldorado Creek Gold Weneedamechanismtoexplainthisdistributionofgold compositionsaroundLoneStar Th following The f ll i model d l provides id an explanation l ti It is based on the behaviour of gold when it is deposited from the mineralizing fluid. f The remaini
Slide 10: Simplified Model for gold mineralization at Lone Star
SimplifiedModelforgoldmineralizationatLoneStar Section through Lone Star ridge Surface Theamountofgolddepositeddecreasesasfluids The amount of gold deposited decreases as fluids Depth Moveawayfromtheirsource Gold-bearing fluids penetrate rocks Lonestar
Slide 11: Simplified Model for gold mineralization at Lone Star
SimplifiedModelforgoldmineralizationatLoneStar Erosiontopresentlandsurface f Bonanza creeek ek Eldorado Cree L LoneStar St Violet Mine
Slide 12: Simplified Model for gold mineralization at Lone Star
Simplified p Model for g gold mineralization at Lone Star Bonanza creeek ek Eldorado Cree L LoneStar St Violet Mine Silver content of gold increases Gold abundance decreases
Slide 13: What about the gold in Eldorado Creek?
What about the gold in Eldorado Creek? Violet LoneStar Mine Mine (trivial) (10,000oz) Sameas 2540%Ag Placer EldoradoCreek 25millionounces The gold in Eldorado creek is derived from Lone Star ridge- NOT the south side of the valley
Slide 14: Lone Star ridge is the most attractive exploration target
Lone Star ridge is the most attractive exploration target in the Eldorado /Bonanza Creek drainage. drainage What about elsewhere in the Klondike? The same approach has been used to identify gold signatures in lode and placer samples
Slide 15: Gold types and evolution of placers: Klondike
Goldtypesandevolutionofplacers:Klondike DAWSONCITY Goldtypesaccordingtocomposition LoneStartype: Lone Star LastChanceandBear Last Chance and Bear KingSolomon Dome Creektype KingSolomonDome T Type 25k SulphurCreekand IndianRivertype
Slide 16: Main Conclusions 1
Main Conclusions; 1 1. All of the placer gold recovered from the Klondike was derived from within the Klondike 2. The coarser-grained placer gold in the Klondike ((including g everything y g that was recovered by ypplacer mining thus far) was all derived from discordant, shallow to steeply dipping q
Slide 17: Main Conclusions 2
Main Conclusions 2 1. Gold composition and grain shape studies indicate that the lode gold sources were mainly localized in four relatively small areas within the Klondike 2 Available 2. A il bl evidence id suggests t that th t there th is i potential for one or more major lode gold deposits p withi