T4 Critical Minerals and Framework Geology: The USGS Earth Mapping Resources Initiative (Earth MRI) and Related Activities I

Sunday, 9 October 2022
8:00 AM - 12:00 PM
601

ECONOMIC MINERAL ASSEMBLAGES OF HEAVY MINERAL SANDS: INSIGHTS FROM THE EARTH MRI VIRGINIA FALL ZONE PLACER FOCUS AREA

Paper number: T4-14
Program: Technical Sessions
Time: 11:20 AM – 11:35 AM

Authors

Abstract

Heavy mineral sand placer deposits containing economic resources of titanium and zirconium are well documented in southeastern Virginia. The surficial geology of Virginia’s Coastal Plain is a result of multiple marine transgressive and regressive sea-level cycles since the Pliocene, which may have preserved other undiscovered placer deposits within Neogene and Quaternary sedimentary units. Utilizing a multi-method top down approach, we assessed available airborne radiometric and stream sediment geochemical data from the National Uranium Resource Evaluation (NURE) datasets to refine target areas for geologic map compilations and new mapping at the 1:100,000-scale, and to complete additional sampling of surficial geologic units to evaluate the presence for titanium minerals, zircon, and monazite. Heavy mineral concentrates indicate higher total heavy mineral (THM) fractions are most common along the Fall Zone in sediments of the Pliocene Cold Harbor formation (Tch, informal unit) and from stream sediment samples draining Neoproterozoic metasedimentary and metavolcanic rocks (Zmsv) of the Roanoke Rapids terrane. The THM content ranges up to 13 percent by weight (wt %) of the bulk sample, and on average, the economic mineral assemblage of the THM fractions is ~81 wt %. Ilmenite, rutile, and zircon are the primary economic minerals present. Monazite was detected at concentrations of less than 2 wt % of the THM fraction in the 20 analyzed mineral concentrates. Rare earth element (REE) trends observed in analyzed samples suggest that other unidentified REE-bearing minerals may be present. Higher percentages of zircon are present in THM concentrates collected in the Fall Zone from the following formations: Zmsv, Tch, and the Bacons Castle Formation (Qbc). Titanium-bearing mineral percentages of the THM concentrates are more variable across the project areas. Geologic maps, cross-sections and a GeMS-compliant geodatabase were created for this project and are publicly available. A second phase of work focusing on the easternmost Piedmont just west of the project area is underway, aiming to understand mineral provenance and critical mineral occurrences within regolith on source rock.

Geological Society of America Abstracts with Programs. Vol. 54, No. 6

doi: 10.1130/abs/2022AM-382422

© Copyright 2022 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.