RECENT ADVANCES IN ANALYTICAL TECHNIQUES IN ORE DEPOSITS RESEARCH

Over the past several years our understanding of ore-forming processes in magmatic-hydrothermal systems has improved significantly. Today we are able to thoroughly characterize the chemical and isotopic compositions of ore-forming fluids, including concentrations of metals in the fluids, as well as determine absolute ages and durations of ore-forming events with a precision that was unprecedented a few decades ago. Improvements in modern microanalytical techniques now permit analysis of metals and other elements at parts per million levels or better in samples in the nanogram to picogram range.

Perhaps the question that has intrigued economic geologists more than any other has been the concentration of metals in ore-forming fluids.  The answer to this question determines, to a large extent, the amounts of fluid and time required to form a deposit. Recent developments involving laser ablation ICP-MS, PIXE, PIGE and synchrotron-based XRF (SXRF) now permit metal contents of individual fluid inclusions to be analyzed. Combined with careful petrography, these data can be used to determine which of several different hydrothermal fluids were transporting and depositing metals. Synchrotron-based XAFS analysis offers the additional possibility of determining the speciation of metals in solution. Analysis of melt inclusions and coeval fluid inclusions is providing valuable information concerning metal contents of silicate melts associated with magmatic-hydrothermal deposits, and mechanisms of transfer of metals from the melt to the hydrothermal fluid. Raman analyses now permit quantitative estimates of volatiles in ore-forming fluids.

Advances in instrumentation and techniques for stable and radiogenic isotopic analysis of ore and gangue minerals and fluid inclusions have led to a more complete understanding of sources of ore fluids and metals in magmatic-hydrothermal deposits. SHRIMP analyses of individual sulfide phases have revealed complex variability in sulfur isotopic composition in many deposit types. Ages and durations of ore-forming events are now routinely determined based on U-Pb, ⁴⁰Ar/³⁹Ar, and Re-Os isotopic systematics. Future collaborations between geochronologists and ore-fluid geochemists are expected to better constrain the temporal evolution of ore-fluid chemistry.