Gold is not the only material captured by the sluice box. There are other minerals that have a high s.g value relative to most rocks, but are not as heavy as gold, known as ‘black sand’.
These minerals (black sand) are usually a mixture of iron oxide (hematite and magnetite), and sometimes ilmenite (titanium iron oxide) or cassiterite (tin oxide). If present in large quantities, these black sands can seriously affect the gold recovery because they inhibit the deposition of gold particles, especially flaking gold particles. In areas rich in black sand, sluice boxes must be cleaned more regularly because gold cannot penetrate the black sand beds that accumulate behind rivers.
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