PROVENANCE AND DRAINAGE DYNAMICS OF BLACK HILLS, SD STREAMS, INTERPRETED FROM HEAVY MINERAL SUITES

A heavy mineral-sediment study was undertaken to investigate the provenance sensitivity and related stream dynamics of drainages throughout the Black Hills in western South Dakota. The region is known for significant gold deposits and the occurrence of historically important pegmatite districts. It was suspected that Black Hills stream systems could be useful in providing distinctive mineral suites as sediment indicators of local provenance and perhaps "pathfinders" of economic mineral potential. Conversely, various characteristics of the sediment populations should yield information related to stream dynamics (relative maturity, etc.).

Field work consisted of sampling sediment from sites along five different stream drainages located in areas of contrasting bedrock, French Creek (east of Custer), Rapid Creek (at Hisega and at Silver City), Whitewood Creek (northeast of Deadwood), Battle Creek (east of Keystone), and Little Elk Creek (in Little Elk Creek Canyon). Gold-panning techniques collected initial grain populations of very coarse (1-2mm)and medium (.25-.5mm)size, as well as raw, unsorted samples from each site. Lab analysis at Wheaton College consisted of 1)general population estimates of grain-type abundances; 2)separation of heavy minerals by density (sodium polytungstate and methylene iodide liquids), magnetic contrasts and color typing; and 3)petrographic identification. The heavy-mineral suites in particular indicate good correlation with bedrock. Grain size and morphology also exhibit properties reflecting contrasts in drainage flow-histories among the streams.