Albert H Hofstra
Al Hofstra is a Research Geologist with the Geology, Geophysics, and Geochemistry Science Center.
Science and Products
Filter Total Items: 76
Integration of new geologic mapping and satellite-derived quartz mapping yields insights into the structure of the Roberts Mountains allochthon applicable to assessments for concealed Carlin-type gold deposits
Geologic mapping and remote sensing across north-central Nevada enable recognition of a thick sheet of Middle and Upper Ordovician Valmy Formation quartzite that structurally overlies folded and faulted Ordovician through Devonian stratigraphic units of the Roberts Mountains allochthon. In the northern Independence Mountains and nearby Double Mountain area, the Valmy Formation is in fault contact
Authors
Christopher S. Holm-Denoma, Albert H. Hofstra, Barnaby W. Rockwell, Paula J. Noble
Shipboard magnetic field "noise" reveals shallow heavy mineral sediment concentrations in Chesapeake Bay
Shipboard magnetic field data collected over Chesapeake Bay exhibit low-amplitude, short-wavelength anomalies that most likely indicate shallow concentrations of heavy mineral sediments. Piston core layers and black sand beach samples exhibit enhanced magnetic susceptibilities and carry remanent magnetization, with mineralogical analyses indicating ilmenite and trace magnetite and/or maghemite and
Authors
Anjana K. Shah, Peter R. Vogt, Joseph G. Rosenbaum, Wayne L. Newell, Thomas M. Cronin, Debra A. Willard, Rick A. Hagen, John Brozena, Albert Hofstra
Mapping argillic and advanced argillic alteration in volcanic rocks, quartzites, and quartz arenites in the western Richfield 1° x 2 ° quadrangle, southwestern Utah, using ASTER satellite data
The Richfield quadrangle in southwestern Utah is known to contain a variety of porphyry Mo, skarn, polymetallic replacement and vein, alunite, and kaolin resources associated with 27-32 Ma calc-alkaline or 12-23 Ma bimodal volcano-plutonic centers in Neoproterozoic to Mesozoic carbonate and siliciclastic rocks. Four scenes of visible to shortwave-infrared image data acquired by the Advanced Spaceb
Authors
Barnaby W. Rockwell, Albert H. Hofstra
Ore genesis constraints on the Idaho Cobalt Belt from fluid inclusion gas, noble gas isotope, and ion ratio analyses
The Idaho cobalt belt is a 60-km-long alignment of deposits composed of cobaltite, Co pyrite, chalcopyrite, and gold with anomalous Nb, Y, Be, and rare-earth elements (REEs) in a quartz-biotite-tourmaline gangue hosted in Mesoproterozoic metasedimentary rocks of the Lemhi Group. It is the largest cobalt resource in the United States with historic production from the Blackbird Mine. All of the depo
Authors
Albert H. Hofstra, Gary P. Landis
Occurrence model for volcanogenic beryllium deposits
Current global and domestic mineral resources of beryllium (Be) for industrial uses are dominated by ores produced from deposits of the volcanogenic Be type. Beryllium deposits of this type can form where hydrothermal fluids interact with fluorine and lithophile-element (uranium, thorium, rubidium, lithium, beryllium, cesium, tantalum, rare earth elements, and tin) enriched volcanic rocks that con
Authors
Nora K. Foley, Albert H. Hofstra, David A. Lindsey, Robert R. Seal, Brian W. Jaskula, Nadine M. Piatak
Lithogeochemistry of the Devonian Popovich Formation in the northern Carlin Trend, Nevada
No abstract available.
Authors
Albert H. Hofstra, William Christiansen, B Zohar, Tousignant
Deep permeable fault–controlled helium transport and limited mantle flux in two extensional geothermal systems in the Great Basin, United States
This study assesses the relative importance of deeply circulating meteoric water and direct mantle fluid inputs on near-surface 3He/4He anomalies reported at the Coso and Beowawe geothermal fields of the western United States. The depth of meteoric fluid circulation is a critical factor that controls the temperature, extent of fluid-rock isotope exchange, and mixing with deeply sourced fluids cont
Authors
Amlan Banerjee, Mark Person, Albert Hofstra, Donald S. Sweetkind, Denis Cohen, Andrew Sabin, Jeff Unruh, George Zyvoloski, Carl W. Gable, Laura Crossey, Karl Karlstrom
Geochemical and stable isotopic data on barren and mineralized drill core in the Devonian Popovich Formation, Screamer sector of the Betze-Post gold deposit, northern Carlin trend, Nevada
The Devonian Popovich Formation is the major host for Carlin-type gold deposits in the northern Carlin trend of Nevada. The Popovich is composed of gray to black, thin-bedded, calcareous to dolomitic mudstone and limestone deposited near the carbonate platform margin. Carlin-type gold deposits are Eocene, disseminated, auriferous pyrite deposits characterized by acid leaching, sulfidation, and sil
Authors
William D. Christiansen, Albert H. Hofstra, Pamela B. Zohar, Gilles Tousignant
Ages and sources of components of Zn-Pb, Cu, precious metal, and platinum group element deposits in the goodsprings district, Clark County, Nevada
The Goodsprings district, Clark County, Nevada, includes zinc-dominant carbonate replacement deposits of probable late Paleozoic age, and lead-dominant carbonate replacement deposits, copper ± precious metal-platinum group element (PGE) deposits, and gold ± silver deposits that are spatially associated with Late Triassic porphyritic intrusions. The district encompasses ~500 km2 although the distri
Authors
Peter G. Vikre, Quentin J. Browne, Robert J. Fleck, Albert H. Hofstra, Joseph L. Wooden
Evaluation of the role of magmatic volatiles from Eocene mafic to felsic igneous rocks in the formation of Carlin-type gold deposits of the Carlin trend and Jerritt Canyon District as constrained by preliminary He, Pb, Sr, and Nd isotopic data
No abstract available.
Authors
Albert H. Hofstra, Gary P. Landis, Wayne R. Premo, M.W. Ressel, Christopher D. Henry
'Forensic' geochemical approaches to constrain the source of Au-Ag in low-sulfidation epithermal ores
In order to better constrain genetic processes involved in forming mineral deposits (and ultimately exploration models), it helps to know from where the metals of interest are derived. How the metals arrived at their point of deposition, and why they were deposited there, are separate issues. We are using three different techniques in an attempt to better understand these processes for epithermal
Authors
James A. Saunders, G. D. Kamenov, Albert H. Hofstra, D. L. Unger, R. A. Creaser, F. Barra
Paleozoic stratigraphy and kinematics of the Roberts Mountains allochthon in the Independence Mountains, northern Nevada
New biostratigraphic, stratigraphic, and structural data from deformed lower Paleozoic sedimentary units of the Roberts Mountains allochthon (RMA), Independence Mountains, Nevada, have enabled the identification of stratigraphic units within the allochthon that range in age from Late Cambrian through Late Devonian. The McAfee thrust fault emplaced a relatively thick (>200 m) sheet of Ordovician Va
Authors
Christopher S. Holm-Denoma, Albert H. Hofstra, Stephen A. Leslie, Paula J. Noble
Science and Products
Filter Total Items: 76
Integration of new geologic mapping and satellite-derived quartz mapping yields insights into the structure of the Roberts Mountains allochthon applicable to assessments for concealed Carlin-type gold deposits
Geologic mapping and remote sensing across north-central Nevada enable recognition of a thick sheet of Middle and Upper Ordovician Valmy Formation quartzite that structurally overlies folded and faulted Ordovician through Devonian stratigraphic units of the Roberts Mountains allochthon. In the northern Independence Mountains and nearby Double Mountain area, the Valmy Formation is in fault contact
Authors
Christopher S. Holm-Denoma, Albert H. Hofstra, Barnaby W. Rockwell, Paula J. Noble
Shipboard magnetic field "noise" reveals shallow heavy mineral sediment concentrations in Chesapeake Bay
Shipboard magnetic field data collected over Chesapeake Bay exhibit low-amplitude, short-wavelength anomalies that most likely indicate shallow concentrations of heavy mineral sediments. Piston core layers and black sand beach samples exhibit enhanced magnetic susceptibilities and carry remanent magnetization, with mineralogical analyses indicating ilmenite and trace magnetite and/or maghemite and
Authors
Anjana K. Shah, Peter R. Vogt, Joseph G. Rosenbaum, Wayne L. Newell, Thomas M. Cronin, Debra A. Willard, Rick A. Hagen, John Brozena, Albert Hofstra
Mapping argillic and advanced argillic alteration in volcanic rocks, quartzites, and quartz arenites in the western Richfield 1° x 2 ° quadrangle, southwestern Utah, using ASTER satellite data
The Richfield quadrangle in southwestern Utah is known to contain a variety of porphyry Mo, skarn, polymetallic replacement and vein, alunite, and kaolin resources associated with 27-32 Ma calc-alkaline or 12-23 Ma bimodal volcano-plutonic centers in Neoproterozoic to Mesozoic carbonate and siliciclastic rocks. Four scenes of visible to shortwave-infrared image data acquired by the Advanced Spaceb
Authors
Barnaby W. Rockwell, Albert H. Hofstra
Ore genesis constraints on the Idaho Cobalt Belt from fluid inclusion gas, noble gas isotope, and ion ratio analyses
The Idaho cobalt belt is a 60-km-long alignment of deposits composed of cobaltite, Co pyrite, chalcopyrite, and gold with anomalous Nb, Y, Be, and rare-earth elements (REEs) in a quartz-biotite-tourmaline gangue hosted in Mesoproterozoic metasedimentary rocks of the Lemhi Group. It is the largest cobalt resource in the United States with historic production from the Blackbird Mine. All of the depo
Authors
Albert H. Hofstra, Gary P. Landis
Occurrence model for volcanogenic beryllium deposits
Current global and domestic mineral resources of beryllium (Be) for industrial uses are dominated by ores produced from deposits of the volcanogenic Be type. Beryllium deposits of this type can form where hydrothermal fluids interact with fluorine and lithophile-element (uranium, thorium, rubidium, lithium, beryllium, cesium, tantalum, rare earth elements, and tin) enriched volcanic rocks that con
Authors
Nora K. Foley, Albert H. Hofstra, David A. Lindsey, Robert R. Seal, Brian W. Jaskula, Nadine M. Piatak
Lithogeochemistry of the Devonian Popovich Formation in the northern Carlin Trend, Nevada
No abstract available.
Authors
Albert H. Hofstra, William Christiansen, B Zohar, Tousignant
Deep permeable fault–controlled helium transport and limited mantle flux in two extensional geothermal systems in the Great Basin, United States
This study assesses the relative importance of deeply circulating meteoric water and direct mantle fluid inputs on near-surface 3He/4He anomalies reported at the Coso and Beowawe geothermal fields of the western United States. The depth of meteoric fluid circulation is a critical factor that controls the temperature, extent of fluid-rock isotope exchange, and mixing with deeply sourced fluids cont
Authors
Amlan Banerjee, Mark Person, Albert Hofstra, Donald S. Sweetkind, Denis Cohen, Andrew Sabin, Jeff Unruh, George Zyvoloski, Carl W. Gable, Laura Crossey, Karl Karlstrom
Geochemical and stable isotopic data on barren and mineralized drill core in the Devonian Popovich Formation, Screamer sector of the Betze-Post gold deposit, northern Carlin trend, Nevada
The Devonian Popovich Formation is the major host for Carlin-type gold deposits in the northern Carlin trend of Nevada. The Popovich is composed of gray to black, thin-bedded, calcareous to dolomitic mudstone and limestone deposited near the carbonate platform margin. Carlin-type gold deposits are Eocene, disseminated, auriferous pyrite deposits characterized by acid leaching, sulfidation, and sil
Authors
William D. Christiansen, Albert H. Hofstra, Pamela B. Zohar, Gilles Tousignant
Ages and sources of components of Zn-Pb, Cu, precious metal, and platinum group element deposits in the goodsprings district, Clark County, Nevada
The Goodsprings district, Clark County, Nevada, includes zinc-dominant carbonate replacement deposits of probable late Paleozoic age, and lead-dominant carbonate replacement deposits, copper ± precious metal-platinum group element (PGE) deposits, and gold ± silver deposits that are spatially associated with Late Triassic porphyritic intrusions. The district encompasses ~500 km2 although the distri
Authors
Peter G. Vikre, Quentin J. Browne, Robert J. Fleck, Albert H. Hofstra, Joseph L. Wooden
Evaluation of the role of magmatic volatiles from Eocene mafic to felsic igneous rocks in the formation of Carlin-type gold deposits of the Carlin trend and Jerritt Canyon District as constrained by preliminary He, Pb, Sr, and Nd isotopic data
No abstract available.
Authors
Albert H. Hofstra, Gary P. Landis, Wayne R. Premo, M.W. Ressel, Christopher D. Henry
'Forensic' geochemical approaches to constrain the source of Au-Ag in low-sulfidation epithermal ores
In order to better constrain genetic processes involved in forming mineral deposits (and ultimately exploration models), it helps to know from where the metals of interest are derived. How the metals arrived at their point of deposition, and why they were deposited there, are separate issues. We are using three different techniques in an attempt to better understand these processes for epithermal
Authors
James A. Saunders, G. D. Kamenov, Albert H. Hofstra, D. L. Unger, R. A. Creaser, F. Barra
Paleozoic stratigraphy and kinematics of the Roberts Mountains allochthon in the Independence Mountains, northern Nevada
New biostratigraphic, stratigraphic, and structural data from deformed lower Paleozoic sedimentary units of the Roberts Mountains allochthon (RMA), Independence Mountains, Nevada, have enabled the identification of stratigraphic units within the allochthon that range in age from Late Cambrian through Late Devonian. The McAfee thrust fault emplaced a relatively thick (>200 m) sheet of Ordovician Va
Authors
Christopher S. Holm-Denoma, Albert H. Hofstra, Stephen A. Leslie, Paula J. Noble