Term
| What would you find if there was a positive gravity anomaly? |
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Definition
High density mafic intrusion - ore deposits formed by gravity settling.
Dense, metallic ore minerals |
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Term
| Where are the five likely sites of deposition of placer minerals? |
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Definition
Meander bends
Plunge pools
Dykes
Confluences
Beaches |
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Term
| What are the 3 key requirements to form a hydrothermal fluid? |
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Definition
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Term
| What is the difference between an ore mineral and a gangue mineral - give examples |
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Definition
An ore mineral is a valuable mineral containing valuable metals - such as gold and cassiterite.
A gangue mineral is a low-value waste mineral, such as Quartz or Calcite |
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Term
| What is the formula for concentration factor? |
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Definition
| Concentration of metal in ore / Average crustal abundance |
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Term
| In gravity settling, what is meant by "Cumulative layer"? |
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Definition
| The layer of dense minerals formed by gravity settling at the base of an intrusion |
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Term
| What does the term "immiscible" mean? |
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Definition
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Term
| What is the difference between Overcast and Underground mining? |
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Definition
| Overcast is mining that is exposed at the surface, where as underground is concealed by overlying ground. |
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Term
| Describe how a grade of copper ore deposited can be increased by the process of secondary enrichment |
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Definition
Above the water table
Rainwater percolates into exposed copper deposit, percolates downwards through pore spaces. In the zone of oxidation (oxygen rich), chemical reactions change insoluble copper sulphides into soluble copper sulfates. Copper sulfates dissolved and carried down in groundwater. Gossan zone left - insoluble, no economic value
Below water table
Copper carried down under water table. Conditions turn from oxidising to reducing - anaerobic. Copper sulfates turned back into insoluble copper sulphides - this is the concentrated copper ore |
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Term
| Describe how uranium ore deposits are formed in sandstone |
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Definition
| Uranium exposed at surface is chemically weathered, carried down in groundwater. Due to changes from oxidising to reducing, uranium ore is deposited as curved rolls at the redox boundary. |
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