Variation in gold content of minerals of the Marysville quartz diorite stock, Montana
Neutron activation analysis for gold has been carried out on 135 mineral samples from throughout the Marysville stock with the following results: (1) the gold content of 44 biotites ranges from 0·002 to 0·924 ppm with an average of 0·076 ppm; (2) 37 hornblende samples gave a range of 0·003–0·823 ppm and an average of 0·100 ppm; (3) for 44 magnetite samples the range was 0·003–0·329 ppm and the average 0·037 ppm; (4) 10 quartz-feldspar samples varied from 0·006 to 0·176 ppm with an average of 0·065 ppm.
High gold values mainly occur near the edge of the stock and the lowest values in the center of the stock. The highest values are found near the old gold mines located along the periphery of the stock.
Because it could not form bonds in crystallizing minerals, the gold was concentrated in the residual fluids of the Marysville magma and was finally deposited in quartz veins at the edge of the stock. The gold in the minerals is probably entrapped as uncharged gold atoms. The amount of gold in a given mineral was determined by the structure of the mineral and the concentration of gold in the magma at the time of crystallization of that mineral.
Mantei, Erwin J., and Arthur H. Brownlow. "Variation in gold content of minerals of the Marysville quartz diorite stock, Montana." Geochimica et Cosmochimica Acta 31, no. 2 (1967): 225-235.
Geochimica et Cosmochimica Acta