Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) has become recognized as a sensitive, effi cient, and cost-effective approach to measuring the major-, minor-, and trace-solute compositions of individual fl uid inclusions in minerals. As a prerequisite for the routine analysis of natural inclusions in our laboratory, the precision and accuracy of the technique was assessed using sets of multi-element synthetic fl uid inclusions. Five multi-element standard solutions were prepared, and incorporated as fl uid inclusions in quartz crystals at 750 °C and 7 kbar. Fluid inclusions were ablated with a 193 nm ArF excimer laser and analyzed with a quadrupole ICP-MS, equipped with an octopole reaction cell for the removal of Ar-based interferences. The internal standard used in all cases was Na. Analytical precision for K, Rb, and Cs is typically better than 15% RSD, whereas Li, Mg, Ca, Sr, Ba, Mn, Fe, Cu, Zn, and Cl analyses are typically reproducible within 30% RSD. Measured concentrations approximate a Gaussian distribution, suggesting that analytical errors are random. Analyses for most elements are accurate within 15%. Limits of detection vary widely according to inclusion volume, but are 1 to 100 µg/g for most elements. These fi gures of merit are in excellent agreement with previous studies. We also demonstrate that, over the range investigated, precision and accuracy are insensitive to inclusion size and depth. Finally, the combination of our LA-ICP-MS analyses with microthermometric data shows that charge-balancing to NaCl-H 2 O equivalent chloride molality is the most valid approach to LA-ICP-MS data reduction, where chloride-dominated fl uid inclusions are concerned.

22This study comprises the first systematic classification of native gold geochemistry within 23 alkalic porphyry Cu-Au systems and the placer expression of such systems. The 24 geochemistry and mineral associations of gold from four alkalic porphyry deposits in British

Porphyry-epithermal and orogenic gold are two of the most important styles of gold-bearing mineralization within orogenic belts. Populations of detrital gold resulting from bulk erosion of such regions may exhibit a compositional continuum wherein Ag, Cu, and Hg in the gold alloy may vary across the full range exhibited by natural gold. This paper describes a new methodology whereby orogenic and porphyry-epithermal gold may be distinguished according to the mineralogy of microscopic inclusions observed within detrital gold particles. A total of 1459 gold grains from hypogene, eluvial, and placer environments around calcalkaline porphyry deposits in Yukon (Nucleus-Revenue, Casino, Sonora Gulch, and Cyprus-Klaza) have been characterized in terms of their alloy compositions (Au, Ag, Cu, and Hg) and their inclusion mineralogy. Despite differences in the evolution of the different magmatic hydrothermal systems, the gold exhibits a clear Bi-Pb-Te-S mineralogy in the inclusion suite, a signature which is either extremely weak or (most commonly) absent in both Yukon orogenic gold and gold from orogenic settings worldwide. Generic systematic compositional changes in ore mineralogy previously identified across the porphyry-epithermal transition have been identified in the corresponding inclusion suites observed in samples from Yukon. However, the Bi-Te association repeatedly observed in gold from the porphyry mineralization persists into the epithermal environment. Ranges of P-T-X conditions are replicated in the geological environments which define generic styles of mineralization. These parameters influence both gold alloy composition and ore mineralogy, of which inclusion suites are a manifestation. Consequently, we propose that this methodology approach can underpin a widely applicable indicator methodology based on detrital gold.

Crustal growth at convergent margins is generally thought to occur through accretion of juvenile arc crust and/ or addition of magmatic material to the edge of a craton (e.g., Rudnick, 1995). Arc-continent collision zones are thus major sites for crustal growth through time (e.g., Brown et al., 2011). Arc accretion generally leads to development of an accretionary orogen, associated magmatism and basin(s) (e.g., Cawood et al., 2009;Draut & Clift, 2012). The evolution of arc-continent collision zones is generally complex and shows a wide-range of variations depending on configuration of continental and arc crusts, and angle and rates of convergence (Brown et al., 2011). There is no simple model that explains the variations observed in modern and ancient arc-continent collisions.In western North America, the development of the northern Cordilleran accretionary orogen began with collision of early Mesozoic peri-Laurentian arcs with the continental margin in latest Triassic to