Distribution, Analysis, and Recovery of Placer Gold from the Porcupine Mining Area, Southeast, Alaska.
The Bureau of Mines (Bureau) and Alaska Divison of Geological and Geophysical Surveys (ADGSS) completed an evaluation of the placer resources of the Porcupine Mining area near Haines, Alaska, during 1985. The Bureau sampled and evaluated the placer deposits, and the ADGGS mapped and geology and summarized the glacial geologic history of the area. This report summarizes the results of the study. Gold was discovered along the Klehini River in 1898. A gold rush ensued that resulted in the discovery of gold on Porcupine Creek and nearby drainages and that has produced 79,650 oz of raw placer gold, most prior to 1936. Three types of placer deposits occur in the area: (1) stream channel gravels, (2) bench placers, and (3) alluvial fans. Organic material from bench deposts were age dated from 2,100 to 2,700 years ago. Each of these deposit types was sampled to estimate resources, identify gold fineness, determine mineral development potential ratings for streams, and calculate optimum screening sizes for use in recovery plants. Identified resources include 932,000 yd3 of gravel rated as having moderate or high mineral development potential. Bulk character studies of gravel from lower Porcupine Creek indicate that washing plants should be designed to screen to minus 1 mesh and recover gold to plus 80 mesh. gold fineness of 13 samples ranged from 669 to 902 and averaged 837.