GROUNDWATER AND GOLD PHIL DYSON Gold discovered in 1851 5,000 - - PowerPoint PPT Presentation

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Jun 10, 2023 26 likes •347 views

GROUNDWATER AND GOLD PHIL DYSON Gold discovered in 1851 5,000 mines - highest concentration in the world Average depth 300 600 metres Many beyond 1,000 metres Victoria hill 1400 metres IN THE BEGINNING In the beginning: Sediments

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GROUNDWATER AND GOLD PHIL DYSON

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Gold discovered in 1851 5,000 mines - highest concentration in the world Average depth 300 – 600 metres Many beyond 1,000 metres Victoria hill 1400 metres

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IN THE BEGINNING

In the beginning: Sediments accumulate on the floor of the Ordovician Sea in Eastern Gondwana between 487 and 442 million years ago

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GONDWANA

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Stratified layers of sediment

Thousands of metres of sand, silt and mud Continental shelf Deep ocean floor Eastern Gondwana Sediment rests on the continental shelf ahead

f flowing down submarine canyons and

stratifying over the deep ocean floor

Turbidites

Of the order of !0 kilometres

Hundreds of kil

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Lancefieldian Bendigonian Chewtonian Castlemanian Yapeenian Darawillian 487 - 442 million years Graptolites rapidly evolve and inhabit the surface of the ancient ocean. When they die they fall to the deep ocean floor and are buried in layers of sediment The species present establish the age of the old rocks with certainty Up to 6,000 metres

f sediment

3 – 4 Km

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FOSSIL HUNTING

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GRAPTOLITE FOSSILS

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GRAPTOLITES

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FOLDING - CRUSTAL SHORTENING IN THE LATE ORDOVICIAN

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FOLDED ROCK

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MARINE SEDIMENT LAYERS NEAR VERTICAL

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BEDROCK

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Folding leads to fracturing which is greatest in fold axes and fault zones Fractures are generally only open to a depth of 50 to 100 metres. Beyond this depth they are closed because of overburden pressures. Groundwater flow is, accordingly, usually much greater in a north-south direction (into the diagram) than it is in an east-west direction (across the diagram).

Anisotropic Fractured Rock Aquifer

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LOCAL SHEAR ZONES

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Quartz reefs rich in gold form in fracture zones in fold axes Reef mining along north-south anticlinal axes reinforces preferential groundwater flow along north-south fold axes

The field fills with groundwater and almost every significant drainage depression becomes a saline groundwater discharge area Significant groundwater discharge occurs as the northerly flow down the old workings discharges to the Myers Creek

Quartz Reefs, Gold and Mining

Quartz Reefs

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Old workings become underground drains that greatly enhance the northward flow of groundwater along anticlinal axes

Groundwater migrates through underground tunnels

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BENDIGO GOLDFIELD 1923

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GROUNDWATER DISCHARGE

ESTIMATED WATERTABLE DEPTH

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CHEMISTRY

SALINITY:

5,000 – 10,000 MG/L
1 TO 2 TEASPOONS IN A LITRE OF WATER
OR 5 TO 10 TONNES PER ML
SEA WATER IS 35,000 MG/L
IRRIGATION WATER <1,500 MG/L

ARSENIC:

2- 6 MG/L
2 – 6 KILOGRAMS PER ML
USA EPA PROTOCOL FOR DRINKING WATER IS 0.01 MG/L

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GROUNDWATER DISCHARGE TO BENDIGO CREEK

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GROUNDWATER DISCHARGE TO BENDIGO CREEK

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BAY STREET GOLDEN SQUARE 2007

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BAY STREET GOLDEN SQUARE 2007

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GROUNDWATER DISCHARGE TO BENDIGO CREEK

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SALT FORMED THROUGH EVAPORATION OF SALINE GROUNDWATER

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SALT DAMAGE

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GROUNDWATER MANAGEMENT

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GROUNDWATER MANAGEMENT

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GROUNDWATER MANAGEMENT

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