Geology topics

Douglas Yager

Publications and source records attributed to Douglas Yager.

7 recordsLinked to original sources

USGS2025

Tracking the sources of metals to the San Juan River, Four Corners Region, USA: An introduction to the thematic issue

Surface water quantity and quality is important for arid and semi-arid regions where many people, including underserved and Indigenous communities, rely on a scarce resource for drinking water, irrigation, livestock and ceremonial uses. The southwestern United States, and specifically the Four Corners Region (Colorado, Arizona, New Mexico and Utah), is an example of this situation. Elevated concentrations of metals including aluminium, arsenic and lead were identified in previous studies and this study in the San Juan River from below the Navajo Dam, through the Navajo Nation to Mexican Hat, Utah. An interdisciplinary team applied approaches and principles of geology, geochemistry, geomorphology, hydrology and statistics to gain a better understanding of the tributaries supplying the source(s) of metals to the San Juan River. This introductory paper provides an overview of the ‘Metal geochemical fingerprinting to identify sub-watershed source contributions to surface water at a regional arid watershed scale, Four Corners Region, USA’ thematic collection . An overview of sampling sites, techniques and potential sources of metals is provided. Approaches used in this study could be applied to investigations in similar systems globally.

Four Corners region↗

USGS2025

Applying geological unit distribution and chemical weathering indices to evaluate potential lithological sources of Al, As and Pb to the San Juan River, Four Corners region, USA

In arid to semi-arid landscapes, sporadic monsoonal events, varying widely in scale and distribution, can generate overland flow resulting in streamflow in ephemeral channels. These channels may contain metal-laden sediments that are a by-product of the weathering and erosion of local geological units. To evaluate the potential for local geology to contribute aluminium (Al), arsenic (As) and lead (Pb) to the San Juan River, northwestern New Mexico, USA, the distributions of geological units were delineated for 12 hydrological basins within the greater San Juan River watershed. Concentrations of Al, As and Pb in the predominant geological units were compiled from data in the National Geochemical Database. Chemical indices of weathering (CIW) were calculated for geological units with greater than 5% coverage in the entire San Juan River watershed. Based on CIWs of the major geological units, the Mesaverde Group (CIW = 95.2), Chinle and Dolores Formations ( combined ) (CIW = 93.3), and Mancos Shale ( combined ) (CIW = 82.6) are the most likely units to weather, erode and contribute sediments with elevated concentrations of Al, As and Pb to the San Juan River. The results of this study show the importance of understanding geological sources of sediments because they could be substantial contributors of constituents of concern to water, especially in arid environments where surface water may be the only source of water in the region.

Arizona, Colorado, New Mexico, Utah↗

USGS2025

Morphometric and geological characterization with statistical correlations for 33 tributary drainage basins of the San Juan River watershed in the Four Corners region, USA

Basin morphometry, climate and geology control how a hydrological network evolves over time, controlling the efficiency of weathering of elements from geological materials, and ultimately the input of sediment and dissolved constituents to river systems. Exceedances to the Navajo Nation surface water quality standards for trace metals have been reported in the San Juan River watershed. Because metals are transported adsorbed to fine-grain sediment, the identification of areas with elevated sources of trace metals and/or areas with increased erosion and sediment transport potential is an important first step in protecting water quality. Physical factors such as elevation, slope, relief and stream order were used to quantify morphometric parameters that effect the contribution of trace metals into the stream network. By correlating these parameters with water quality data that were collected from tributaries along the San Juan River, we identified statistically significant regressions between morphometric parameters and total Al, Pb, U, Fe and Mn in surface water. Positive correlations with trace metals include tributary drainage basin perimeter, pour point elevation and total number of streams, while negative correlations include stream length ratio, ruggedness number and longest basin axis. Stream reach measurements within geological units that contain known trace metal constituents reveal that Gallegos Canyon and Desert Creek are the most susceptible to sediment mobilization and transport, while other tributary drainage basins, such as Desert, Recapture and Salt creeks, are associated with naturally elevated concentrations of Al, As, Pb and U.

Arizona, Colorado, New Mexico, Utah↗

USGS2024

Deep resistivity geophysics of the San Juan–Silverton caldera complex, San Juan County, Colorado (USA)

Magnetotelluric (MT) and audiomagnetotelluric (AMT) data are used to better understand the subsurface geology and mineral resources in the San Juan–Silverton caldera complex located near Silverton, Colorado, western United States, as part of the extensive southern Rocky Mountains volcanic field that covers much of southwestern Colorado and northern New Mexico. Seven MT and AMT profiles of varying lengths image resistivity structure to depths of ~5 km. The AMT inversion models characterize geophysical responses of near-surface lithologies, structures, and mineralized systems and also help corroborate airborne electromagnetic data at shallow levels. The MT inversion models extend our depth of investigation from near the surface to great depths (~5 km) and help to form hypotheses about roots of the hydrothermal plumbing that fed shallower mineralized systems. Subsurface high resistivities occur beneath intermediate-composition lava flows and Proterozoic units. Subsurface moderate- to low-resistivity values may reflect hydrothermal plumbing that served as flow paths for mineralizing fluids and metallic ore formation. The model interpretations presented in this study could be utilized in remediation planning or mineral resource applications. The methods used could be applied to other watersheds with similar volcanic environments containing acid-generating historical mines or hydrothermally altered and mineralized source rocks.

Colorado↗

USGS2023

Geophysical data provide three dimensional insights into porphyry copper systems in the Silverton caldera, Colorado, USA

The Silverton caldera in southwest Colorado, USA hosts polymetallic veins and pervasively altered rocks indicative of porphyry copper systems. Nearly a kilometer of erosion has exposed multiple levels of the hydrothermal systems from shallow lithocaps down to quartz-sericite-pyrite veins. New airborne electromagnetic and magnetic survey data are integrated with previous alteration mapping and porphyry models to show the subsurface geophysical response of shallow to deep levels of the porphyry system. Qualitative map views show lateral changes in the magnetization and resistivity of the hydrothermally altered rocks. The volcanic terrain exhibits high magnetization and high amplitude anomalies map near-surface plutonic rocks associated with porphyry systems. Magnetic susceptibility measurements on outcrops of hydrothermally altered rocks indicate magnetite content decreases upward and outward from the source intrusions where magnetic anomaly lows are observed over the lithocaps. The resistivity maps highlight hydrothermal alteration as resistivity lows with exception being rocks having propylitic alteration. Quantitative resistivity models show low resistivity zones with an apparent thickness around 50–150 m beneath quartz-sericite-pyrite veins interpreted to be the result of supergene processes that may continue today, and the calculated magnetic source depths occur near the top of this zone. The resistivity models also show rocks having propylitic, silicic, and quartz-alunite-pyrophyllite assemblages exhibit high resistivity with depth, and argillic alteration assemblages had high resistivity due to high quartz content. This integrated approach presented in a three-dimensional environment provides guidance when exploring for porphyry copper systems in less exposed terrains.

Colorado↗

USGS2023

Resistivity imaging over porphyry copper systems in the Red Mountain district, southwest Colorado, USA

The Red Mountain district in southwestern Colorado produced base and precious metals hosted in breccia pipes and vein structures related to an extensive lithocap that overlies pervasive quartz-sericite-pyrite alteration. A helicopter-borne time-domain electromagnetic survey flown over the district yielded resistivity values that range from tens to thousand or more ohm-m, with lesser resistivity values in the lithocap and greater resistivity values in the rocks with propylitic alteration. A 60 m-thick, low resistivity zone subparallel to topography characterizes the magmatic-hydrothermal breccia pipes. A broad zone of low resistivity that may envelope epithermal deposits spans multiple flight lines and occurs beneath rocks with argillic alteration. A 50 m-thick low resistivity zone occurs beneath quartz-sericite-pyrite alteration and may indicate porphyry deposit at depth.

Colorado↗

USGS2022

A novel method for conducting a geoenvironmental assessment of undiscovered ISR-amenable uranium Resources: Proof-of-concept in the Texas Coastal Plain

A geoenvironmental assessment methodology was developed to estimate waste quantities and disturbances that could be associated with the extraction of undiscovered uranium resources and identify areas on the landscape where uranium and other constituents of potential concern (COPCs) that may co-occur with uranium deposits in this region are likely to persist, if introduced into the environment. Prior to this work, a method was lacking to quantitively assess the environmental aspects associated with potential development of undiscovered uranium resources at a scale of a uranium resource assessment. The mining method of in situ recovery (ISR) was historically used to extract uranium from deposits in the Goliad Sand of the Texas Coastal Plain. For this reason, the study’s methodology projected the following types of wastes and disturbances commonly associated with ISR based on historical ISR mining records: the mine area, affected aquifer volume, mine pore volume, water pumped and disposed during uranium extraction and restoration, and radon emissions. Within the tract permissive for the occurrence of undiscovered uranium resources, maps and statistics of factors were derived that indicate the potential contaminant pathways. The percentage of days meeting the criteria for air stagnation indicate the potential for radon accumulation; the geochemical mobility of COPCs in groundwater in combination with effective recharge indicates the potential for infiltration of surface-derived COPCs; the geochemical mobility of COPCs in groundwater combined with hydraulic conductivity indicates the propensity for transmitting fluids away from contaminated or mined aquifers; and finally, geochemical mobility of COPCs in surface water combined with the factor for climatic erosivity (R factor) indicates the potential for COPCs to persist in surface waters due to runoff. This work resulted in a new methodology that can be applied to any undiscovered mineral resource to better understand possible wastes and disturbances associated with extraction and identify areas on the landscape where COPCs are likely to persist.

Texas↗