Experimental and fluid inclusion constraints on the ore metal content and origin of volatiles associated with large NI-CU--PGE deposits
By: by Hanley, Jacob James.
Published: 2006
Language: eng
Number of pages: 285
ISBN-13: 9780494160107
Description: Microanalyses of synthetic fluid inclusions containing a S-free, NaCl brine (20-70 wt% eq. NaCl) that was reacted with silicate melt and Pt and Au metal at T=600-800&deg;C, P=1.5 kbar show that both metals are significantly soluble (  Cfluidmetal  1-103 ppm) at moderately oxidizing (Ni-NiO) conditions, and partition strongly into the fluid phase (  Dfluid/meltmetal  = 102-103). Maximum dissolved Pt and Au concentrations decrease by &sim;2 log units with increasing salinity from 20 to 70 wt% eq. NaCl. Maximum dissolved Au concentrations increase approximately &sim;1 log unit for every 100&deg;C increase in brine temperature. The negative correlation between trapped metal concentration and salinity may be the result of the "salting-out" of neutral metal complexes [e.g., aqueous PtCl3H or Pt(OH)2-(H2On) as the NaCl0 content increases in the fluid and free H2O is consumed. Due most likely to slow metal-fluid-melt equilibrium, microanalysis of fluids trapped using synthetic fluid inclusion methods allows only semi-quantitative estimation of minimum (non-equilibrium) precious metal solubility.Microanalyses of fluid inclusions from the footwall Cu-Ni-PGE systems at Sudbury, Canada, and pegmatites and cumulate rocks below the J-M reef in the Stillwater Complex, U.S.A. show that Na-Ca-K-Fe-Mn-Ba-Pb-Sr-Zn-rich brines (&sim;30-80 wt% eq. NaCl) and non-aqueous volatiles (CH4 vapour; liquid/supercritical CO2; halide melt) carried ppm concentrations of precious/accessory metals (Pt, Pd, Au, Ag, Sn, Ag, Bi) and up to wt% concentrations of base metals (Cu) at the time of their entrapment. Volatile P-T-X characteristics show major similarities at Sudbury and Stillwater, notably evidence for carbonic fluid-brine immiscibility and the selective partitioning of ore metals into the carbonic fluid phase. Inclusion assemblages record a prolonged evolution of volatiles. At near-solidus conditions, inclusions trapped C and Cl-rich volatiles that exsolved from and coexisted with a high Cl/H2O residual silicate liquid or fractionated sulfide liquid at &sim;700-800&deg;C. At post-cumulus conditions, inclusions trapped hybrid fluid compositions derived by the interaction of magmatic brines with crystalline wall-rocks, sulfides, or groundwater, and later modified by carbonic fluid-brine immiscibility and metal reprecipitation. Ore metals in the volatiles were derived through interaction with PGE-bearing sulfide assemblages or possibly by the partitioning of ore metals from sulfide liquid.
Notes: Source: Dissertation Abstracts International, Volume: 67-07, Section: B, page: 3653.

Thesis (Ph.D.)--University of Toronto, 2006.

Includes bibliographic references.

Electronic version licensed for access by U. of T. users.