http://www.sciencedirect.com/science/article/pii/S1674987111000806

Zoned tourmaline (schorl-dravite) in the matrix of hydrothermal explosive breccia and oreveins in gold deposits, Chita region, Eastern Transbaikalia, Russia, are associated with Na- and K-richporphyry-type subvolcanic intrusives. d18O values of tourmaline from three gold deposits (Darasun,Talatui, Teremkinskoye) are t8.3&, t7.6&, and t6.0& and calculated d18O values of fluids responsiblefor the tourmalinization are t7.3&, t7.7&, and t4.2&, respectively. These data imply an igneousfluid source, except at the Teremkin deposit where mixing with meteoric water is indicated. Wide rangesof Fe3t/Fetot and the presence of vacancies characterize the Darasun deposit tourmaline indicating wideranges of f (O2) and pH of mineralizing fluids. Initial stage tourmalines from the gold deposits of theDarasun ore district are dravite or high mg schorl. Second stage tourmaline is characterized by oscillatoryzoning but with Fe generally increasing towards crystal rims indicating decreasing temperature. Third stage tourmaline formed unzoned crystals with xMg (mole fraction of Mg) close to that of the first stagetourmaline, due to a close association with pyrite and arsenopyrite. From Fe3t/Fetot values, chemical compositionand crystallization temperatures, logf(O2) of mineralizing fluids ranged from ca. 25 to 20,much higher than for the gold-bearing beresiteelistvenite association, indicating that tourmalinizationwas not related to gold mineralization.