Metamorphic water plots as a larger box the result of analyzing hydrous minerals which are a mixture from igneous and sedimentary protoliths. That is geothermal waters show and enrichment in 18 O relative to meteoric waters from nearby streams, whereas 2 H shows no similar trend. Since little H is present in the rocks there is no similar H isotope shift. This is a powerful argument to support those geologists who feel that most hydrothermal waters are of meteoric origin and not evolved from magmas. In the latter case, the geothermal waters should plot on the magmatic rectangle.
Figure shows the oxygen isotopic ratios of some ore deposits.
Note they plot all over the diagram. This indicates there must be a significant meteoric water component. Sulfur - important because sulfur is the dominant anion in many ore deposits and sulfur isotopes can often tell us the source of the sulfur. Deposit is of organic origin and due to bacterial reduction. Wild fluctuations of values between various layers coincides with extinctions.