Eastern Mineral Resources Team, USGS

Residual deposits, including laterites, bauxites, clays, weathered crusts and soils, comprise unconventional resources for rare elements,
including

Residual deposits are, in general, much less well-understood compared to more conventional resources.

This project will investigate

the geochemical and mineralogical distribution of these elements in high alumina alteration systems,
and the processes that lead to their concentration in residual deposits that form in-situ by partial to complete weathering of igneous bedrock.

The investigation results will be used to develop models for these unconventional rare element resources. This research will focus on the rare earth element-Ga-Sn-In-W geochemistry of weathered crusts, soils, and clay deposits (e.g., Foley et al., 2002; Foley, 2012) associated with fractionated A-type igneous systems of the Southern Appalachians Mountains of Virginia, North Carolina, South Carolina and Georgia, (e.g., Tollo et al., 2004) with an emphasis on identifying potential HREE(heavy rare earth elements)-dominated deposits that resemble the ion-adsorption clay deposits of South China (Wu et al., 1996, Wu and Ishihara, 1994). The rare earth elements Ga, In, Sn, and W contents of weathered equivalents are thought to reflect a combination of parent lithochemistry and surficial weathering processes. Features that are expected to exert control on the contents of trace elements in residual deposits include source rock composition, mineralogy, solution chemistry, and weathering history (e.g., Foley and Ayuso, 2008).

The Appalachian Mountains contain voluminous, deeply weathered Neoproterozoic-Phanerozoic anorogenic metaluminous-to-peralkaline granitoids (e.g., Robertson River batholith, Irish Creek pluton, Virginia). A-type granites typically have highly silicic compositions with high contents of Be, F, Ga, In, Nb, Zr, rare earth elements, Sn, Ta, and Y. Granitic rocks of the southeastern US have been subjected to a long history of intense differential chemical weathering and saprolitization, comparable to that of South China and Southeast Asia -- areas which contain important examples of residual deposits (see Wilson, 2004; Wu et al. 1996), e.g., heavy-rare-earth-element clay deposits at Longnan, China. Little is currently known about the occurrence of associated rare metals, such as Ga, In, and W, in any residual deposits formed from highly weathered granite.

Unconventional Resources of Rare Elements:

The Bearing of Source and Process on the Genesis of Residual Deposits

Statement of the problem:

Mineral Resources	Eastern / Central / Western / Alaska / National Minerals Information
	Crustal Geophysics and Geochemistry / Spatial Data