Roles of regional structures and country-rock facies in defining mineral belts in central Idaho mineral province with detail for Yellow Pine and Thunder Mountain mining districts

Karen Lund; John N. Aleinikoff; Christopher S. Holm-Denoma

doi:10.3133/pp1884

Home/Archive/USGS

USGS · pp1884

Roles of regional structures and country-rock facies in defining mineral belts in central Idaho mineral province with detail for Yellow Pine and Thunder Mountain mining districts

Karen Lund·John N. Aleinikoff·Christopher S. Holm-Denoma

View original source ↗Read source document ↗Export metadata ↓

Abstract

The central Idaho metallogenic province hosts numerous mineral deposit types. These include Late Cretaceous precious-polymetallic vein deposits, amagmatic Paleocene–Eocene breccia-hosted gold-tungsten-antimony deposits, and Eocene mercury deposits in metasedimentary roof pendants and in Late Cretaceous granitoids. Hot-springs gold deposits in Eocene volcanic rocks are also included in the central Idaho province. New sensitive high mass-resolution ion microprobe (SHRIMP) uranium-lead (U-Pb) ages for igneous rocks and for detrital zircon analyses of metasedimentary rocks along with geologic mapping clarify the geologic framework of the mineral deposits. This framework includes (1) structural controls for regional distribution of mining districts, (2) progressive structural development of individual districts, (3) regional sedimentary facies and their control of metals associations resulting in regional belts, and (4) influences of the several regional magmatic events. In central Idaho, 15 mining districts form two clusters that are grouped about a 200-kilometer (km) long system of normal faults. The northwestern cluster is in the regional hanging wall west of large, west-side-down faults, and the mineral deposits are located along smaller faults and fractures that cut the regional hanging wall. The southeastern cluster is in the regional hanging wall east of a linked large east-side-down fault and along and controlled by related hanging wall faults. At the southern extent of the regional fault system, the Yellow Pine-Thunder Mountain districts span a nearly 24-km-wide, east-tilted crustal block of normal-fault dominoes, exposing original crustal depths from 5 to 10 km deep on the west in the Late Cretaceous to shallow-surface depths on the east in the Eocene. Ore deposition in the northwestern district cluster was primarily Late Cretaceous and related to Idaho batholith plutons with only a single deposit related to a small Eocene intrusion; in the southeastern cluster, most deposits were initiated in the Late Cretaceous but with varying manifestations of overprinted Eocene mineralization activity. In the Yellow Pine-Thunder Mountain districts at the southern extent of the southern cluster, several mineralizing pulses occurred during hanging-wall collapse, such that (1) early deposits were multiply overprinted and (2) deposit depths, ages, and structural characteristics change progressively eastward. Originally deep-seated western Yellow Pine district deposits are Late Cretaceous viscoplastic mesothermal veins overprinted by Paleocene and Eocene breccia-hosted epithermal deposits. Central Yellow Pine district deposits contain early deeper vein systems but are primarily Paleocene and Eocene breccia-hosted epithermal deposits in Late Cretaceous plutonic rocks and Proterozoic–Paleozoic roof pendant rocks. Eastern district deposits are Eocene hot-springs-related deposits in the roof pendant. Thunder Mountain deposits farthest east are near-surface hot-springs deposits in Eocene volcanic and volcaniclastic rocks that overlie buried Cretaceous igneous and older roof pendant rocks. The mining district clusters are sited across several northwest-striking paleostratigraphic belts that are exposed in roof pendants and are offset by the regional normal fault system. A northeastern belt is Mesoproterozoic strata associated with gold-silver-copper±cobalt deposits. A central belt of Neoproterozoic rocks is not associated with mineral deposits in the central Idaho mineral province. A southwestern belt composed of probable Paleozoic deep-water miogeoclinal slope rocks and late Paleozoic epicratonic basinal rocks is thin and narrowly exposed but associated with gold-silver-antimony-tungsten±mercury deposits. These metasedimentary rocks (and their metal associations) are parts of regional mineral belts in which metal endowments are related to particular sedimentary facies belts and their Cretaceous thrust-fault juxtaposition and where these features have proximity to Late Cretaceous or Eocene igneous rocks. Offset and preservation or erosional stripping of these facies belts, thrust plates, igneous settings, and the associated regional mineral belts were controlled by the sense and magnitude of displacements across the regional normal-fault system.

Explore related subjects

Professional Paper Report

Source-reported bounding extent: 43° to 47° latitude; -117° to -112° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

Karen Lund, John N. Aleinikoff, Christopher S. Holm-Denoma. 2023-08-29. Roles of regional structures and country-rock facies in defining mineral belts in central Idaho mineral province with detail for Yellow Pine and Thunder Mountain mining districts. https://doi.org/10.3133/pp1884

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related USGS reports

USGS2026

Allostratigraphy and formalizing the Cold Harbor Alloformation, Virginia Coastal Plain, Eastern Virginia

Introduction Distinct morphologic features in the Virginia part of the Coastal Plain Province (herein referred to as the Virginia Coastal Plain) were noted in one of the earliest geologic surveys in 1839 (Rogers, 1884). South of the James River, Rogers (1884, p. 252) described a western bench that ranged from “a low rocky coast…of the primeval sea” to an eastern facing scarp east of the City of Suffolk, Virginia. His eastern bench extended from the scarp at Suffolk, which he suggested was a former shoreline, to the present Atlantic Ocean. Notably, the eastern plain was described as less dissected than the western plain. In Virginia, creation and publication of topographic maps by the U. S. Geological Survey began in the mid-1880s. By 1905, many areas in eastern Virginia were mapped as 30-minute and 15-minute series with 10-foot (ft) contour interval accuracy (Virginia Division of Mineral Resources [VDMR] , 2008). After the continued release of these early maps that displayed Virginia Coastal Plain morphology in increasingly greater detail, several geological reports were published where scarps and plains were traced, named, and origins proposed (Shaler, 1890; Shattuck, 1901; Clark and Miller, 1906, 1912; Wentworth, 1930). Shattuck (1901) recognized three continuous scarps in Maryland and most importantly suggested that there was a correlation between surficial deposits (geologic formations) and morphologic terraces; this defined the terrace-formation concept that became the basis of geologic mapping of the Upper Pliocene and Pleistocene sediments in the Virginia Coastal Plain. Clark and Miller (1912) described three Pleistocene formations and supported the terrace-formation concept because the sediments within each formation were lithologically similar to one another, and differentiating them by comparing key vertical sections was not helpful. In Virginia, Wentworth (1930) defined and mapped five Pleistocene terraces on the basis of correlating morphologic terraces with their underlying formation sediments. Similarly, Cooke (1931) identified and traced seven marine shorelines and proposed corresponding terrace names from Maryland to Florida. Cooke (1931) also pointed out that the various elevations of scarps were related to interglacial sea-level highstands whereas prior workers called on vertical land movement of emergence and submergence to create shoreline scarps. Cooke’s (1936) geologic map of eastern South Carolina showing the Pleistocene sediments is also based on the terrace-formation concept. Detailed geologic mapping of the Virginia Coastal Plain by Virginia Division of Mineral Resources (VDMR) and U.S. Geological Survey (USGS) followed lithostratigraphic convention for Early Pliocene and older marine sediments. However, geologic mapping of Upper Pliocene and Pleistocene sediments used the concept of morphologic setting and elevations of scarp toe and flat-plain, or the terrace-formation concept. The 1983 version of the North American Stratigraphic Code (hereafter the Code) (North American Commission on Stratigraphic Nomenclature [NACSN] , 1983) introduced allostratigraphy that gave credence to the terrace-formation concept. According to the current Code (NACSN, 2021; Article 58), “an allostratigraphic unit is a mappable body of rock that is defined and identified on the basis of its bounding discontinuities,” and, “formal allostratigraphic units may be defined or distinguish between different (1) superposed discontinuity-bounded deposits of similar lithology, (2) contiguous discontinuity-bounded deposits of similar lithology, or (3) geographically separated discontinuity-bounded units of similar lithology…The lithology of an allostratigraphic unit plays no part in its definition.” However, definition and placement of bounding discontinuities relies on lateral and vertical knowledge of lithology and is so recognized in Article 58e, “A type locality and type area must be designated; a composite stratotype or a type section and several reference sections are desirable.” We understand that each of the terrace formations of Late Pliocene and Pleistocene age were deposited during a marine transgressive event tied to an interglacial sea-level highstand (scarp above the Poquoson Member of the Tabb Formation may be the result of a still-stand as sea level was falling after deposition of the Lynnhaven Member, refer to fig. 1). The base of each map unit is an unconformity (or is at least in part for the base of the Poquoson) and nomenclature for each unit might be changed from “formation” to “alloformation,” as suggested by Doar and Berquist (2009). Figure 1 shows the relative placement of these mapped and named alloformations as used in the Virginia Coastal Plain and Fall Zone (a zone of transition between the Piedmont and Coastal Plain Provinces) (Berquist, 2021). Except perhaps for the Poquoson, many of these proposed alloformations are unlikely to interfinger or grade laterally seaward into extensive deep marine sediments. After their deposition, erosion during sea-level fall and then rise for the next depositional event would seemingly obliterate any marine connection without a basal unconformity. All these alloformations contain sediments deposited in fluvial, estuarine, and shallow-marine environments and are bound everywhere by unconformities. This paper documents the Cold Harbor Alloformation as a formal stratigraphic unit and the rationale for mapping the sediments using an allostratigraphic classification. The Cold Harbor Alloformation is composed of sediments from a variety of environments such as gravel beds, shoreline beach sands, marsh and estuarine sand and mud, and shallow marine sands. These sediments are found at elevations up to 240 ft and lie unconformably above older sediments and rocks. Our work relied on observations of outcrops and many auger borings to identify basal unconformities.

Virginia↗

USGS2026

Formalization of the Elsing Green Alloformation, Virginia Coastal Plain, Eastern Virginia

The Elsing Green Alloformation is herein formalized as a new Pleistocene alloformation in the Virginia Coastal Plain. This allostratigraphic unit is characterized by an unconformity-bounded terrace deposit occupying a morphologic flat with a mapped elevation range of about 26 to 38 feet (7.9 to 11.6 meters); its landward extent is commonly marked at the base of an erosional scarp where the toe is typically at 38 feet (11.6 meters) and is distinguished by its topographic expression and stratigraphic position. Sediments of this unit were previously mapped as part of the Shirley Formation or Sedgefield Member of the Tabb Formation but differ significantly in their bounding scarps and terrace morphology. The type area is within the Tunstall 7.5-minute quadrangle near Elsing Green Plantation, King William County, Virginia. The reference section is provided by boring 2012270-2. Correlation is proposed with other mid-Pleistocene terrace deposits in the mid-Atlantic Coastal Plain, including the younger Lynch Heights Formation of Delaware and the Butlers Bluff Member of the Nassawadox Formation of the Eastern Shore of Virginia. The age of the Elsing Green Alloformation is interpreted to be Marine Isotope Stage 9e (about 330,000 years).

Virginia↗

USGS2026

Resurvey of the Marble Canyon and Bridge Canyon dam sites in Grand Canyon National Park—Changes in sediment storage and evidence supporting the occurrence of bedrock incision through the mid-20th century

The Bureau of Reclamation developed an extensive plan for a network of dams, water tunnels, and hydropower plants in and around Grand Canyon, Arizona, in the 1940s through 1960s. The two largest of these planned dams were the Marble Canyon and Bridge Canyon Dams on the Colorado River. Though these dams were ultimately never built, Reclamation conducted extensive topographic, bathymetric, and subsurface exploration work at the sites proposed for these dams in the 1940s and 1950s. Resurveys of these dam sites were conducted between 1998 and 2021 to determine the changes in sediment storage at these dam sites caused by the upstream construction and operation of Glen Canyon Dam and by the recession of Lake Mead, the reservoir impounded by Hoover Dam. The resurveys of the Marble Canyon dam sites indicate that the post-1950s changes in sediment storage at these dam sites are broadly consistent with flux-based estimates of voluminous sand erosion from Marble Canyon since the 1963 closure of Glen Canyon Dam. These resurveys also suggest that the pre-dam longitudinal variation in sediment thickness over bedrock played a key role in determining the locations of the sand erosion induced by Glen Canyon Dam; more sand eroded from locations where more sand was present in the 1950s. The resurvey of the Bridge Canyon dam sites indicates that the Colorado River’s incision of the Lake Mead delta is regulated both by bed-sediment grain size and downstream hydraulic controls. Finally, analyses of bed-sediment thickness and sedimentological data at the dam sites, and observations of bed scour and gravel transport, suggest that sufficient bedrock was exposed to allow bedrock incision during commonly recurring pre-dam snowmelt floods that entrained small boulders into transport.

Arizona↗