Comparative petrologic evolution of the Sn and W granites of the Fairbanks-Circle area, interior Alaska

Abstract

Late Cretaceous to Early Tertiary granitic plutons associated with W skarn or Sn greisen-skarn occur interspersed in a belt 70x 200-km-long just northeast of Fairbanks, Alaska. All plutons intrude the late Precambrian-early Paleozoic Yukon-Tanana terrane and are similar in major-element compositions (dominantly granodiorite to monzogranite), initial Sr isotopic ratios (0.710 to 0.719), and Pb isotopic signatures ( 206 Pb/ 204 Pb = 19.17 to 19.37). Biotite compositions and opaque mineral abundances indicate both types of plutons crystallized along a buffered path intermediate between nickel-nickel oxide and quartz-magnetite-fayalite. Both suites contain multiple igneous units, with younger, usually equigranular, units spatially related to mineralized zones. Isotopic, trace-element, and mineralogical data suggest an "I-type," "ilmenite-series" classification for both pluton suites. Because the W and Sn plutons appear to represent magmas with similar origins and source materials, differences in observed metallogeny are thought to be related to differences in environment of crystallization and vapor loss. Such differences include: age (102 to 87 Ma for W plutons, 73 to 50 Ma for Sn plutons), crystallization pressure (1 to 2 kbar for W plutons, <0.5 kbar for Sn plutons), vapor loss history (late for the W plutons and early + late for the Sn plutons), and fluorine trends (decreasing F with increasing differentiation for the W plutons and increasing F for the Sn plutons). Differences in confining pressure (depth) and vapor loss history are associated with differences in age: the younger (Sn) plutons are shallower, and the older (W) plutons are deeper. Trace-element patterns (e.g., Rb, B, Be, W, Sn, Li) are similar for least differentiated units of both pluton types, increasing modestly with increasing differentiation for the W plutons and increasing strongly for the Sn plutons. Data are most compatible with 80 to 95 percent fractionation (crystal-liquid) followed by vapor loss for the W plutons and 80 to 90 percnt fractionation (crystal-liquid) for the Sn plutons, with early vapor loss followed by (liquid-liquid?) "ultrafractionation." Ultrafractionation and subsequent ore element enrichment occurs in the Sn plutons by early vapor loss and subsequent F enrichment in the residual magma. The data suggest that metallogeny differences for W vs. Sn plutons in our study area are not a function of differences in initial metal contents of the magmas but are more likely due to differences in magmatic evolution.

Mineralogical and geochemical characteristics of scheelite-bearing skarns, and genetic relations between skarn mineralization and petrogenesis of the associated granitoid pluton at Sargipali, Sundergarh District, Eastern India

“…Broad correlation between igneous composition and skarn type with respect to their metal contents has been described by several workers (Meinert, 1983;Newberry and Swanson, 1986;Newberry, 1987;Newberry et al, 1990;Meinert, 1993Meinert, , 1995Meinert, , 1997Newberry, 1998;Kuşcu et al, 2002;Öztűrk et al, 2005). According to Meinert et al (2005), tungsten skarns are associated with coarse-grained, generally unaltered, equigranular intrusions (with pegmatite and aplite dykes).…”

Geology and geochemistry of the Mendejin plutonicrocks, Mianeh, Iran

“…Cross-cutting relationships and the increasing dip of the volcanic layers in the vicinity of the contacts indicate that Mendejin pluton was emplaced forcefully. It is believed that the volcanic activity occurred along Newberry et al, 1990), peraluminous (C) and medium to high potassium calc-alkaline (D) features of the Mendejin plutonic rocks. Fig.…”

An approach to geochemical characterization of productive versus barren granitoids in terms of iron in Central Turkey

“…These studies also suggest the possibility of discriminating the productive and barren plutonic rocks based on the assumption that the granitic magma is the main source of hydrothermal fluids for the ore elements. Recent studies along these lines have presented well-defined connections between major metal types and various magmatic rocks ranging from diorite to granite (Shimazaki, 1980;Meinert, 1983Meinert, , 1995Newberry, 1987;Newberry et al, 1990;Meinert, 1990;Paktunc, 1990;Ishihara and Sasaki, 1991;Naldrett, 1992;Blevin and Chappell, 1992;Srivastava and Sinha, 1997;Nicolescu et al, 1999). These studies provide strong evidence for a genetic relationship between magmatic processes and mineralization, and also for examining the predictable relationship between mineral deposits and the degree of differentiation of the related granitoids.…”