Despite its small size, Hong Kong has a relatively large number of mineral occurrences. Some mineral deposits have been exploited commercially. Metalliferous mineral occurrences are grouped into four broad categories: tin-tungsten-molybdenum mineralisation, copper-lead-zinc mineralisation, iron mineralisation and placer deposits of tin and gold. Mesozoic igneous activity is largely responsible for this diversity of mineral deposits and the mineral concentrations have been variably enhanced by hydrothermal activity associated with faulting. Concentrations of non-metalliferous minerals that have been commercially exploited include kaolin clay, feldspar, quartz, beryl and graphite.