SOIL ANALYSIS BY HANDHELD LASER-INDUCED BREAKDOWN SPECTROSCOPY (LIBS) FOR IDENTIFICATION OF BURIED PEGMATITE

Li-pegmatite exploration is challenging in terrains where outcrop is sparse or entirely lacking. On the premise that rock weathering within the critical zone will impart a bedrock geochemical signature to the saprolite and soil developed upon it, we have undertaken a feasibility study to determine if LIBS analysis of the deep Kanhapludult soils developed across the Carolina Tin-Spodumene Belt (CTSB) can be used to identify the presence of mineralized pegmatite in the shallow surface. The CTSB is a domain of albite-spodumene pegmatites of Carboniferous age located in the Inner Piedmont physiographic province that was the most historically important Li pegmatite district in North America and is presently the focus of renewed exploration. Drill holes on Piedmont Lithium’s Carolina Lithium Prospect (CLP) near Bessemer City in Gaston County, NC have intersected >75 spodumene mineralized pegmatite bodies estimated to comprise a resource of greater than 44Mt at 1.09% Li2O; one of the largest pegmatite Li resource in the United States. Outcrop of mineralized pegmatite across the CLP is modest, as mineralized pegmatites are primarily sheet-like structures of limited surface outcrop. Because spodumene-bearing pegmatites across the CTSB are characterized by mica with higher Li contents and lower K/Rb ratios than more common unmineralized quartz-feldspar pegmatites, elevated values of Li in soil would provide a signature for the presence of mineralized pegmatites at depth and it may be possible to identify spodumene-mineralized pegmatites on the basis of soil Li-K/Rb systematics. With this mind, we have undertaken realtime analysis in the field of Li, K, and Rb by handhald laser induced breakdown spectroscopy (LIBS) in soils mapped as the Lloyd Series developed across the CLP. An initial single 175mlong traverse observed a modest elevation in Li content passing over an inferred subsurface mineralized pegmatite. Subsequently, a 200m-long grid traverse was conducted across a second area overlying a mineralized pegmatite known to be present from drilling at <20m depth. The central portion of this multi-leg traverse observed a rise in soil Li content from 0.3 to >0.6 wt. % passing over the subsurface dike that was accompanied by a coincident decline in K/Rb ratio, features that were present but subdued in magnitude along adjacent traverses further distant from the mineralized pegmatite.