ABSTRACT
The Liese zone is a recently discovered high-grade gold deposit on the Pogo claims, approximately 90 miles (145 km) southeast of Fairbanks. A conservative geologic resource for the Liese zone is 9.98 million tons at an average grade of 0.52 oz/t, for a total of 5.2 million contained ounces.
The region is underlain by highly deformed, amphibolite-grade paragneiss and minor orthogneiss of the Late Proterozoic(?) to middle Paleozoic Yukon-Tanana terrane, which has been intruded by Cretaceous felsic granitoid bodies thought to be related to gold mineralization in the Fairbanks area and elsewhere along the Tintina gold belt.
The Liese zone is hosted primarily in gneiss, and lies approximately 1.5 km south of the southern margin of the Late Cretaceous Goodpaster batholith. Mineralization occurs in three or more tabular, gently dipping quartz bodies, designated L1 (uppermost), L2, and L3 (lowermost). The thickness of the quartz bodies ranges from 1 to 20 m, averaging approximately 7 m. The quartz contains approximately 3 percent ore minerals, including pyrite, pyrrhotite, loellingite, arsenopyrite, chalcopyrite, bismuthinite, various Ag-Pb-Bi ± S minerals, maldonite, native bismuth, and native gold. Early biotite and later quartz-sericite-stockwork and sericite-dolomite alteration are spatially associated with the Liese zone, which shows characteristics of both vein and replacement styles of mineralization. Geochemical data indicate a strong correlation between gold and bismuth, and weaker correlations between gold, silver, and arsenic. Based on U-Pb dating of intrusive rocks, the Liese zone was formed between 107 and 94.5 m.y. ago, although 40Ar/39Ar cooling ages on alteration minerals return younger ages of 91 Ma, suggesting a protracted or multiphase thermal history. The Liese zone may represent a deep-seated manifestation of the "intrusion-related" gold deposit type.
Characteristics of Gold Mineralization at the Ciurug Vein, Pongkor Gold-Silver Deposit, West Java, Indonesia
