NEW GEOLOGIC MAPS: Earth Mapping Resources Initiative (EARTH MRI) – Mountain Pass

Earth Mapping Resources Initiative (EARTH MRI)

MOUNTAIN PASS REE FOCUS AREA

Andrew V. Zuza, Michael H. Darin, and Seth Dee

NBMG recently completed two new geologic maps, a technical report, and GeMS database conversions of published geologic maps as part of the Mountain Pass REE Focus Area of the USGS Earth MRI initiative. Mountain Pass, CA contains one of the richest REE deposits in the world hosted in Proterozoic gneiss and alkaline granitic rocks. Exposures of Proterozoic orthogneiss extend southward from Mountain Pass in a narrow band that straddles the Nevada / California border, southwest of Las Vegas, NV. In Nevada, these Proterozoic rocks are present in the northern New York Mountains, southern McCullough Range, and Lucy Gray Mountains. Mapping was conducted at 1:24,000 scale, in conjunction with geochemical analyses and geochronology, to provide lithological and structural constraints on the potential distribution of REE deposits beyond Mountain Pass. The mapping depicts six distinct Paleoproterozoic orthogneiss units with new U-Pb ages spanning ca. 1622 to 1675 Ma. Strongly deformed potassic granitic orthogneiss yielded ages of 1657 to 1672 Ma and less-to-undeformed granite yielded ages of ca. 1641 Ma, which brackets deformation between 1.66 Ga and 1.64 Ga. The Paleoproterozoic rocks are unconformably overlain by Tertiary volcanic and sedimentary strata that are deformed by largely north-striking normal faults that accommodated middle to late Miocene tilting and extension, and north-northwest-striking oblique-normal faults that were active during a later phase of deformation in the latest Miocene to Pliocene. Evidence for Quaternary faulting is limited to a set of north- and northeast-striking faults along the western flank of the Lucy Gray Range that displace alluvial fan deposits as young as early Pleistocene. Despite similar Paleoproterozoic bedrock as Mountain Pass, CA, our study did not reveal conditions favorable for an economically significant REE deposit in southern NV.

Title: Geologic map of the Nevada part of the Desert quadrangle and adjacent part of the McCullough Mountain quadrangle, Clark County, Nevada

Author: Michael H. Darin, Andrew V. Zuza, Seth Dee, and Racheal L. Johnsen
Year: 2022
Series: Open-File Report 2022-07
Version:
Format: map: 36 x 26 inches, color; text: 37 pages, one page in color
Scale: 1:24,000

Title: Geologic map of the southern half of the McCullough Mountain quadrangle, Clark County, Nevada

Author: Andrew V. Zuza, Michael H. Darin, and Seth Dee
Year: 2022
Series: Open-File Report 2022-08
Version:
Format: map: 34 x 21 inches, color; text: 32 pages, some color
Scale: 1:24,000

Learn more about the Earth Mapping Resources Initiative (EARTH MRI) here: https://nbmg.unr.edu/Maps&Data/EarthMRI.html