Paper No. 15
Presentation Time: 8:00 AM-12:00 PM
LA-ICP-MS MICROANALYSIS OF SINGLE FLUID INCLUSIONS FROM INTRUSION-RELATED GOLD DEPOSITS, TINTINA GOLD PROVINCE, ALASKA AND YUKON
Microthermometric study of fluid inclusions in quartz from gold deposits and occurrences of the Tintina gold province, Alaska and Yukon, has shown the ore-forming fluids to be universally CO2-rich and of variable, but typically low to moderate salinity. Laser-ablation ICP-MS microanalysis was applied to some of the studied inclusions to obtain quantitative estimates of the relative abundances of a variety of ore-related trace elements. Analyses were carried out using a 193 nm ArF Lamda Physic Excimer laser coupled with an Agilent 7500c ICP-MS. Single fluid inclusions from intrusion-related gold systems (IRGS) at Fort Knox, Scheelite Dome, and Clear Creek were analyzed simultaneously for K, Mn, Fe, As, and Sb; followed by K, Ca, Ag, Pb, and Bi; and, finally, K, Ag, Pb, Cu, Zn, and Li. Element ratio measurements (all to Na) range from 0.01-0.06 for As and 0.004-0.03 for Sb in Fort Knox intrusion-hosted quartz veins, but one extremely gold-rich quartz peg vein had a ratio as high as 0.37 for As. In addition, whereas most Bi ratios were ?0.01, one inclusion within the peg vein had a ratio of 0.67 within an inclusion. Base metal ratios were consistently <0.01 for Pb, and 0.01-0.05 for Cu and Zn. Similar values characterized fluid inclusions from sheeted veins within the Scheelite Dome and Clear Creek intrusions, but inclusions from auriferous veins in adjacent hornfels at Scheelite Dome commonly showed As, Pb, and Sb ratios >1. Data from reconnaissance examination of several other significant gold deposits, but of more controversial origin, were compared and contrasted with those from the definitive IRGS. At Donlin Creek, inclusions from the main gold resource at the Lewis ore zone exhibited highly anomalous ratios of 4-15 for As and 3-5 for Fe, and elevated ratios of 0.1-0.3 for Sb, whereas those from the sub-economic Dome property were 0.004-0.016, 0.026-0.079, and 0.001-0.003 respectively. It is unclear as to whether the Donlin Creek ore fluids were indeed exceptionally anomalous or if perhaps significant dissolution of abundant fine-grained As- and Sb-bearing sulfide phases within the quartz veinlets occurred. Analysis of a couple of inclusions from the Pogo deposit showed no obvious distinction from those that typified the IRGS.