An update on skarn deposits of Alaska

Abstract

In 1985-with the considerable assistance of Gar Pessel and Janice Hagen-I released "a compendium of data for skarn deposits of Alaska". This work was primarily a literature review and compilation, with some skarn mineral compositions determined by XRD techniques. The compilation showed, among other facts, that there were some serious holes in our knowledge about Alaskan skarns. Since that time the ADGGS has supported Alaskan skarn studies with field assistance, analyses, and microprobe time. I present in this PDF data from these studies over the period 1985-1995. Additional data are given in UAF student theses listed in the references at the end of this document. All the data are also on "quattro" files available with this PDF. Since 1985 a new category of skarn deposit has been recognized, the Gold skarn. This deposit type contains high gold concentrations with relatively low concentrations of Cu and W and is commonly highly anomalous in Te, Bi, As, and Sb (Meinert, 1989). Many Alaskan lode deposits have been mined exclusively for their contained gold, even when other ore elements are present at high concentrations, and skarns are no exception to this tendancy. Hence, production statistics alone are not a good guide to the metal contents-and thus skarn classification-of Alaskan skarns. I have reveised the classification of Alaskan skarns from Newberry (1985) by separating out Au and Mo skarns, employing bulk ore analyses (where available) and otherwise analyses of (representative?) skarn hand specimens and listed these in Table 1.. Scores of additional skarn occurrences have been discovered andlor revealed in the last decade, due to extensive government and industry mapping in Alaska, and these are also listed in Table 1. In this and the following Tables, the skarn types are listed by the following abbreviations: a=Au, c=Cu, f=Fe-(Cu,Au), g=magnesian Fe, m=Mo, s=Sn, w=W, and Z=Zn-Pb. Replacement bodies spatially associated with minor skarn and plutonic rocks (e.g., Liberty Bell, S-Central Alaska) are included in this compilation, but sulfides in marble with no obvious plutonic association (e.g., Reef Ridge, Medfra quadrangle) are not. Table 2 contains a listing of geochemical analyses of skarn samples performed between 1985 and 1995 and not published elsewhere. These were performed by a variety of techniques at several different analytical laboratories, including AA at the ADGGS analytical facility (now defunct), XRF at the University of Alaska, and ICP, AA, INAA, and graphite furnace AA at several commercial laboratories. Data generated by methods of known unreliability (e.g., Sn and W by ICP) are not included in Table 2. Duplicate analyses of several dozen samples by several different reliable techniques (e.g., W by INAA and XRF, Zn by INAA, ICP, AA, and XRF) indicate that the data are generally accurate to better than +I-30%. The samples are derived from a variety of sources: ADGGS pulps previously analyzed for a few elements, samples I collected, and samples donated by ADGGS, USGS, USBM, UAF, and industry ge...

Geochemistry and Origin of Scheelites from the Xiaoyao Tungsten Skarn Deposit in the Jiangnan Tungsten Belt, SE China

“…The scheelite at Xiaoyao has a wide range of WO 3 Figure 6a). [30], the Jitoushan and Baizhangya tungsten deposits [9], the King-Island-oxidized skarn deposit [17], the Kara-oxidized skarn deposit [31], and the Los-Santos-reduced skarn deposit [32]. [30], the Jitoushan and Baizhangya tungsten deposits [9], the King-Island-oxidized skarn deposit [17], the Kara-oxidized skarn deposit [31], and the Los-Santos-reduced skarn deposit [32].…”

“…Sch1b in the distal zone has lower MoO 3 contents of 0.38-0.42% ( Table 2 and Figure 8B). The carbonaceous wall rocks may lessen the effects of such a relatively oxidized magma [17,18]. However, the lack of association between molybdenite and Sch1b under reduced conditions suggests that the ore solution may be already depleted in molybdenum and/or under low f S 2 conditions [34].…”

“…The late oxidized Mo-rich granodiorite dike overprints the sample location of Sch2b (Figure 3), and Sch2b and Sch3 have the same REE patterns with ore-related granodiorite (Figure 7d,f). The elevated Mo content may be provided by the high oxidation state, as well as an overprinting or remobilization of the oxidized Mo-rich magmatic-hydrothermal system [17]. However, Sch2a and Sch4 have low MoO 3 contents (1.71-3.51% and 0.19-0.76%, respectively), accompanied by MoS 2 precipitation ( Figure 8C,H).…”

“…The replacement of garnet released large amounts of calcium ion into the ore-forming fluid and thus raised the activity of calcium ion in solution. Consequently, this led to a disequilibrium between precipitated scheelite and evolving fluids [16,17]. In addition, the W contents of garnet from the Xiaoyao deposit are [9], Xitian [38]; the reduced tungsten skarn deposits, including the Zhuxi [15], Xianglushan [14], Kyanigan [39].…”

“…Despite the extensive literature on trace elements in scheelite, only a few studies focus on tungsten skarn deposits [12][13][14][15]. Most tungsten skarn deposits are characterized by multiple scheelite generations which underwent dissolution and re-precipitation processes [16][17][18]. The superimposition of multiple scheelite generations complicates study on the ore-forming processes via the trace element chemistry of scheelite.…”