The presence of colloidal gold in epithermal mineralizing fluids

Abstract

Transport of gold and silver as colloidal particles has been observed in c. 300 degrees C low salinity fluids from the Arapucandere intermediate sulphidation epithermal base-metal-Au deposit in NW Turkey. Large euhedral quartz crystals, grew after the deposition of sulfides. Overgrowths have a fibrous texture which grew perpendicular to the existing crystal faces and facilitated trapping of large elongate fluid inclusions between the quartz fibres. Episodic trapping of fluid inclusions occurred throughout the growth of quartz. Trapped within primary fluid inclusions are numerous particles of gold, the largest observed is c. 1 mu m but most are smaller. BSE element mapping show these to contain Au, Ag, Cu + Hg. LA-ICP-MS ablation of fluid inclusions confirms Au and Ag is not present in solution, occurring as numerous particles. The concentration of gold in fluid inclusions is orders of magnitude greater than has been previously measured or thought likely in crustal fluids. The average Ag concentration is c. 32 ppm and Au is c. 41 ppm, but the maximum concentrations may reach several 100's to 1000 ppm. Au-Ag particles could not have precipitated in the fluid inclusions, therefore have precipitated elsewhere and transported by the hydrothermal fluid.

C1 [Bozkaya, GUlcan; Bozkaya, Omer] Pamukkale Univ, Dept Geol Engn, Pamukkale, Turkey.

[Banks, David A.] Univ Leeds, Sch Earth & Environm, Leeds, W Yorkshire, England.