EXPLORING TEXTURAL VARIATIONS OF SPODUMENE IN LITHIUM-CESIUM-TANTALUM (LCT) PEGMATITES FROM FLORENCE COUNTY, WISCONSIN, USA

As lithium is increasingly needed for electric car batteries, new resources must be discovered and explored to meet the demands. This study focuses on new occurrences of spodumene, the primary Li ore mineral. In particular, we are aiming to understand the association between coarse magmatic spodumene (CMS) and spodumene-quartz intergrowths (SQI) found together at outcrop and microscopic scales of observation. The King’s X2 and Price Lake dikes are > 50 m long and 1-7 m wide, intruding discordantly in early Proterozoic amphibolites. They belong to the Florence Co. pegmatite field and are situated ~4-5 km from the Bush Lake granite, the closest potential parental granite. Primary magmatic minerals spodumene and amblygonite-montebrasite (Li phosphate) are coeval with K-feldspar, quartz, albite, and elbaite-schorl tourmaline. The primary assemblage is overprinted by albitization products, varying from fine-grain albite masses to coarser, platy albite (cleavelandite) aggregates. Classic SQI is defined as a secondary texture, resulting from the breakdown of the petalite (Li-silicate), however, petalite is absent in these two dikes. Instead, the close association between SQI and CMS suggests that this distinct texture formed from the progressive dissolution, replacement, and recrystallization of CMS, possibly during late hydrofracturing and albitization.

We integrated large-sample slabbing along three orthogonal directions for a 3D overview of mineral textures; laser-induced breakdown spectroscopy (LIBS) to further assess the distribution of Li minerals in the rock slices and their Li contents; transmitted and reflected-light petrography and scanning electron microscopy energy-dispersive X-ray spectroscopy (SEM-EDS) to document the primary and secondary minerals in thin-sections; and cathodoluminescence (CL) imaging to qualitatively assess trace-element differences among spodumene textures. The primary CMS approaches the stoichiometric 3.7 % Li concentrations and is bright orange in CL, whereas secondary spodumene in SQI appears slightly depleted in Li and displays complex dissolution and recrystallization zoning from orange to yellow and pink. The CMS is partly replaced by albite-mica rims and cookeite (Li chlorite) along fractures, whereas SQI is typically unaltered.