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Weathering of copper-bearing minerals produces a wide halo of staining (called a gossan) by secondary copper minerals – often blue-green malachite as in this rock on Kawau Island. The presence of such copper staining is a useful exploration tool, but the presence of economic amounts of ore can only be tested by drilling down into unweathered rock.
Te whakamahi i tēnei tūemi
Private collection
by Eric Coppard
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