TARGETING AREAS OF GOLD FAVORABILITY THROUGH FACTOR ANALYSIS OF STREAM SEDIMENT DATA, FAIRBANKS MINING DISTRICT, EAST-CENTRAL ALASKA

The Fairbanks mining district is located within the Tintina gold province in east-central Alaska. The district is composed of structurally distinct metamorphic terranes and is dominated by Paleozoic sedimentary and volcanic rocks of the Fairbanks Schist. Gold deposits and prospects in the region are mainly gold-bearing quartz veins, with variable abundances of pyrite, arsenopyrite, galena, stibnite, tetrahedrite, and scheelite, in shear zones cutting the schist or Cretaceous intrusions. The district is also host to one operating gold mine at the Fort Knox intrusion-related gold system, where sheeted auriferous quartz veins are hosted in the cupola of a reduced ca. 90 Ma intrusion.

In 1981, the Alaska Department of Geological and Geophysical Surveys (ADGGS) completed a detailed geochemical survey in the Fairbanks mining district. Stream sediment samples were collected and analyzed for copper, lead, zinc, silver, and arsenic. Additional analyses were carried out on select samples for tungsten, gold, mercury, molybdenum, and tin. In 1995, the U.S. Geological Survey re-analyzed the ADGGS samples using multi-element techniques resulting in data for 49 elements. This data set makes it possible to test the ability of factor analyses to outline areas of gold mineralization and target new areas of high gold favorability.

R-mode factor analysis with varimax rotation was performed on log-transformed data for 22 elements. The factor analysis identified seven factors that explain greater than 70% of the total variance. Gold loads highly with arsenic, antimony, and lead, which is consistent with the mineralogy of the orogenic gold vein deposits in the Fairbanks mining district, and the highest factor scores are spatially associated with known vein gold occurrences. Samples that lode highly onto this factor do not correlate with the Fort Knox gold deposit. The samples draining the Fort Knox deposit lode highly onto a factor that correlates with outcropping Late Cretaceous plutonic rocks. This factor does not have a gold signature, however the samples draining Fort Knox do contain detectible gold. Therefore, drainages in the district with samples that lode highly onto this factor, and have detectible gold values, represent exploration targets for additional Fort Knox style intrusion-related gold mineralization.