Peter Modreski | U.S. Geological Survey (original) (raw)

Papers by Peter Modreski

An unusual suite of ferric iron-bearing minerals occurs in xenoliths within a dacite pumice brecc... more An unusual suite of ferric iron-bearing minerals occurs in xenoliths within a dacite pumice breccia. The 33-m.y.-old dacite pumice and ash flow, part of the Mogollon-Datil volcanic field, crops out along NM-12 approximately 1.5 mi (2.4 km) west of Old Horse Springs. The flow is as much as 200 m thick and crops out sporadically within a north-south belt up to 5 km wide and 20 km long.

2002 New Mexico Mineral Symposium, Proceedings Volume

Turquoise is not a well-known gem material from Colorado, but the state has four localities that ... more Turquoise is not a well-known gem material from Colorado, but the state has four localities that have produced significant amounts of turquoise in the past, two of which are still worked today. All the deposits are associated with Tertiary-age felsic igneous rocks, though at Leadville and Cripple Creek the productive turquoise veins are hosted by adjacent Precambrian granite. The turquoise occurs as near-surface supergene veins and veinlets, which are characteristically free of other normally common secondary copper minerals such as azurite, malachite, or chrysocolla. The King turquoise mine is in Conejos County, in the San Luis Valley, about 9 mi east of Manassa and 19 mi west of the town of San Luis. The workings are in a hill composed of chalky, hydrothermally altered silicic volcanic rock, part of the Conejos Formation of Oligocene age. Turquoise was discovered here by Israel Pervoise King in 1890, but extensive Native American workings already existed and tools made of stone and horn have been found here (Harvey and Harvey, 1938). The most extensive mining took place in the 1940s and included open cuts, inclines, and shafts. An 8.75-lb nugget was reported to have been recovered in 1941 (Pearl, 1951). The property is still worked sporadically by Bill King of Manassa, who markets silver jewelry set with the material. Polished turquoise from the mine includes blue-green material intergrown with brown limonitic matrix in an attractive pattern, and sky-blue turquoise that tends to be more solid but does require some stabilization treatment (King, pers. comm. 2002).

1980 New Mexico Mineral Symposium, Proceedings Volume

Open-file report /, 1994

The Elk alkaline massif is one of a group of intrusive centers within the crystalline basement of... more The Elk alkaline massif is one of a group of intrusive centers within the crystalline basement of the Precambrian Baltic Shield in northeastern Poland. The Elk massif is composed mainly of syenite; it is about 400 km2 in areal extent and is buried beneath 800-900 m of Mesozoic and Cenozoic sedimentary rocks. Nine drill holes have been bored into rocks of the massif since 1954. This report describes the results of a joint study of core samples from seven of these drill holes, including major-and minorelement analyses, petrographic and cathodoluminescence observations, and electron microprobe mineral analyses. Thirty-one chemically analyzed core samples comprise five lithologic types: nepheline-sodalite-cancrinite-aegirine syenite (foidbearing syenite), foid-less aegirine-augite syenite (foid-less syenite), aegirine-arfvedsonite syenite (amphibole syenite), quartz-bearing syenite (quartz syenite), and monzogabbro. Some of the rocks show evidence of incipient fenitization, which results in major modifications of their original alkali and silica contents. Clinopyroxene in the rocks ranges from augite in monzogabbro, to aegirine-augite in the foid-less syenite, to highly sodic aegirine in the feldspathoidal syenite (XAC = 0.61-98) and arfvedsonite syenite. Clinopyroxenes in some of the syenite and feldspathoidal syenites are notably zoned, with aegirine-augite cores surrounded by more sodic rims. Biotite is partly altered to chlorite. Increasing Mn enrichment in biotite is observed in the more felsic and feldspathoid-rich rocks. One monzogabbro contains sparse orthopyroxene (Enys). Blue-green to yellow pleochroic amphiboles in the aegirine-arfvedsonite syenite are sodiumand fluorine-rich arfvedsonite. Monzogabbro contains greenish-brown, calcic hornblende. In addition to nepheline, sodalite, and cancrinite, the feldspathoidal syenite contains analcime, natrolite, and perhaps thomsonite. Many of the syenitic rocks contain phenocrysts of microperthite composed of orthoclase and albite, plus late-appearing, interstitial albite. Orthoclase exhibits bright-red cathodoluminescence as does late albite in the arfvedsonite syenite; albite in other syenites luminesces pink to blue. Feldspars in quartz syenite and monzogabbro luminesce blue to bluish green. Monzogabbro contains zoned plagioclase phenocrysts, and sanidine, more sodic plagioclase, and quartz in some samples. 1 All rock types are sodic except quartz syenite, which is potassic, in terms of CaO:Na2O:K2 O ratios. Nepheline and arfvedsonite syenites are peralkaline; foid-less syenite is metaluminous to weakly peralkaline, and quartz syenite and monzogabbro are metaluminous. Agpaitic indexes (mol. Na2O + K2O > AI2 O3) range from 1.01 to1.24 in nepheline syenite, 1.09 to 1.14 in arfvedsonite syenite, 0.94 to 1.02 in foid-less syenite, 0.82 to 0.97 In quartz syenite, and 0.43 to 0.51 in monzogabbro. However, mineralogical characteristics of these rocks are more similar to miaskitic syenites. Differentiation indexes range from 76.53 to 95.37 for syenites and from 44.22 to 47.32 for monzogabbro. All analyzed rocks show light rare-earth-element enrichment, but rare-earth-element fractionation trends are variable. Most rocks have negative Eu anomalies, although three samples have positive Eu anomalies, and monzogabbro and unaltered quartz syenite have no Eu anomalies. The Elk rocks may represent more than one magmatic differentiation series, although this interpretation is complicated by late-to postmagmatic alteration involving introduction of albite, orthoclase, amphibole, sericite, chlorite, and carbonate; some syenites may be fenitized. Absence of a protolith for the fenitized rocks and contacts between various lithologies in the drill core complicate efforts of determining the origin of the Elk massif rocks.

American Journal of Science, May 1, 1973

Open-file report /, 1998

The U.S. Geological Survey, in cooperation with the Bureau of Land Management, Geological Survey ... more The U.S. Geological Survey, in cooperation with the Bureau of Land Management, Geological Survey of Wyoming, and U.S. Bureau of Mines, has produced an estimate of the amount of available coal in an area about 35 miles south of Gillette, Wyoming, where the Wyodak coal bed is, in places, more than 100 ft thick. Available coal is coal that actually is accessible for development under current regulatory, land-use, and technologic conditions. This first western coal availability study, in the Hilight quadrangle, has shown that approximately 60% (2.7 billion short tons) of the total 4.4 billion tons of original coal resources in the quadrangle is available for development. Of this total 4.4 billion tons, 2.9 billion tons are contained in the Main Wyodak coal bed; 67% (1.9 billion tons) of this coal bed is considered available. Local coal-development considerations include dwellings, railroads, pipelines, power lines, wildlife habitat (eagles), alluvial valley floors, cemeteries, the Hilight oil and gas field, and the Hilight gas plant. Some of these considerations would be mitigated so that surface mining could proceed; others presently preclude mining in their vicinity.

Open-file report /, 1986

During the Holocene, the natural combustion of coal seams in the western United States has produc... more During the Holocene, the natural combustion of coal seams in the western United States has produced large amounts of intensely altered sedimentary rock overlying the burning coal. This thermal alteration has heated the rocks to temperatures of 1300°C or higher, as inferred from the mineral assemblages. Such temperatures are achieved by no other common metamorphic process at atmospheric pressure. As a result the altered rocks contain unusual, hightemperature mineral phases. In cases of extreme high temperature, an ironrich liquid slag forms, separates from the parent rock, and then accumulates by flowing into puddles. The slag specimens analyzed have an overall iron oxide content of 35-40 percent, with Fe+^ about ten times the abundance of Fe. Chemically, the slag might be likened to an iron-rich basalt or andesite. Conditions of intense heating coupled with rapid cooling are reflected in the mineralogy of the slag, with examples such as exsolution/oxidation lamellar intergrowths between hematite and magnetite, with Ti concentrated in the hematite, Mg in the magnetite, and both containing significant Al. At least four iron oxide phases can be identified in the slag. Flowing at slightly above its melting point, the slag forms drip-like structures where it flows into a cooler zone of the fire and quickly cools, preserving the shape of the drops. Fe-Mg oxide crystals located toward the outside of the slag droplets contain up to 15 weight percent ZnO. The likely source of the Zn is release from coal in or sediments adjacent to the burning seam; it is likely that other volatile trace metals from the coal may be incorporated into the slag as well. The bulk iron content of the sedimentary rocks overlying the coal appears insufficient to produce the iron-rich slag; large quantities of these rocks with their relatively low and well-disseminated iron content would be needed. Instead, local enrichments of iron, such as in pyrite or iron-rich concretions in the rock overlying the coal, likely provided the iron to produce the slag.

Rocks and minerals, Aug 1, 2002

oin us for a gemstone tour around Colorado! Our field trip J takes us from east to west in the sa... more oin us for a gemstone tour around Colorado! Our field trip J takes us from east to west in the same way you may have toured through Colorado on a mineral collecting trip. This route, from the plains to the mountains, allows us to examine geological settings in proximity to one another and compare different types and ages of rocks where gemstones are known to occur. We cannot discuss every Colorado gemstone occurrence; rather, this is a general review of classic localities with some key references. Most of the deposits are well known, and much has been published about them, as described in Minerals of Colorado (Eckel 1997); therefore, to avoid repetition, only selected or the latest references are given. Emphasis is on any new information-for example, the peridot discovery in Park County and updates on property ownership and accessibility. Many people come to Colorado to gp in the field and collect minerals. When Minerals of Colorado was published, 774 mineral species from Colorado were described, and a few new ones have since been added to the list. There are many good specimen localities in the state, but only a few places yield actual gem material-finding a superior-quality sample that can be transformed into a cut and polished gem is most rare! The original scientific and popular interest in the state’s minerals coincided with the development of industry. Colorado was founded on the search for and production of preciousmetal deposits-gold and silver. During the course of metal mining, numerous splendid mineral crystals were found and saved, but gemstones from the hard-rock mines were all but unknown. However, during the latter part of the nineteenth century, gemstones and crystal specimens came to be known from the state’s granite pegmatites. Smoky quartz, ammonite, and topaz were discovered and eagerly sought around Crystal Peak and other parts of the Pikes Peak region beginning in the 1870s, and in the 1880s aquamarine, smoky quartz, and the associated feldspar and topaz were found on Mount Antero. More mineral occurrences were discovered when Colorado’s pegmatites were investigated for beryl and rare-earth species prior to World War 11, but most of the gem-crystal occurrences were already known by that time. The majority of Colorado’s gemstone occurrences are related to pegmatites rather than hydrothermal vein deposits, with rhodochrosite being a notable exception. Although the best-known pegmatites occur within the Pikes Peak batholith (Raines 2001), pegmatites also are associated with older episodes of granitic intrusion in Colorado. Gemstones, as defined here, are minerals with superior qualities of color and clarity that are durable and large enough to be fashioned for ornamental purposes. Gem usually refers to the material after it is cut and polished. For faceted gems to be

Physics and chemistry of the earth, 1975

To Investigate the proposal that kimberlites and associated rocks originate by anatexIs of mantle... more To Investigate the proposal that kimberlites and associated rocks originate by anatexIs of mantle pendotlte in a H 2 O-and COrrich environment, phase relationships offour peridotite (lherzolite) nodules and one websterite nodule were investigated to 12OD"C and 30 kbar in the presence of H 2 0 and H 2 O-C0 2 vapors with controlled oxygen fugacIty. Solidus temperatures, which are a function of vanous parameters including bulk composition, total pressure. and a H20 , are considerably (12D-2OD°e) lower than previous determinations. Melting of garnet lherzolIte, even in the presence of a vapor of 50/50 mol.~~H 2 0/C0 2 (XH;o = 0.5). begins at depths of less than 150 km beneath the continental shields. This Investigation was augmented by a study of the stabilIty of phlogopite in the system K 2 0-MgO-CaO-AI20rSIOrH20 to 35 kbar at PeH,O <1; P T and-PT' The reactIOn phlogopite + enstatite" + dlOpslde"~forsterite + pyrope + liquid occurs at about 1350°C at 35 kbar. These temperatures are considerably higher than those of the vapor-saturated solIdil of the peridotite nodules, reflecting the absence of Fe and Na and the very low values of aH2 0 ' In expenments with the nodules, phlogopite appeared only when the compositions were spiked with phlogopite. Amphiboles occurred in all experiments with the nodules at pressures below 20-25 kbar. These amphiboles become enriched in pargasite component relative to tschermakite component with increasIng pressure and decreasing temperature. Temperatures indIcated by the compositions of orthopyroxenes coexisting with clInopyroxenes are approximately IOD°C lower than those obtained from previously publIshed pyroxene geothermometers. LIquids under condItions of XH;o~0.6 are nch in Si0 2 and mimic andeSItes. For more CO 2-rich composItIOns. liquIds are usually nepheline normatIve and rich in CaO and A1 2 0 3 • resembling melilitite lavas, which commonly accompany kimberlites.

El Summary El Character and setting El Identified resources El Mineral resource potential E2 Intr... more El Summary El Character and setting El Identified resources El Mineral resource potential E2 Introduction E3 Investigation by the U.S. Bureau of Mines E3 Investigation by the U.S. Geological Survey E5 Appraisal of identified resources E5 Previous investigations E5 Exploration, development, and mining history E5 Coal E5 Uranium E6 Oil and gas E6 Resource appraisal E8 Coal E8 Analytical data E8 Resources E8 Mineral economics E10 Titaniferous sandstone E10 Common industrial minerals £12 Conclusions E12 Assessment of potential for undiscovered resources E12 Geology E12 Description of rock units E13 Geochemistry E13 Sampling methods E13 Analytical methods E14 Results of study E14 Geophysics E15 Gravity data E16 Aeromagnetic data E16 Radiometric data £16 Mineral and energy resources E16 Coal £17 Humate E19 Oil and gas E19 Titaniferous sandstone E19 Uranium E19 Other commodities £20 References cited E20 Appendix £23 Contents

Eolian processes and deposits in the southwestern U.S. Integrated studies to evaluate impacts fro... more Eolian processes and deposits in the southwestern U.S. Integrated studies to evaluate impacts from climatic variability and land use .

Open-File Report, 1990

V and Ag. The average V content of 21 samples is 2.2%, and that of Ag is 400 ppm. Such enrichment... more V and Ag. The average V content of 21 samples is 2.2%, and that of Ag is 400 ppm. Such enrichment is unknown from the primary (reduced) ore of breccia pipes on the North Rim, and only minor enrichment has been documented in two primary orebodies on the South Rim, one of them the Orphan mine. Both elements, however, are consistently enriched in the oxidized zone over breccia pipes, including those sampled over the North Rim orebodies; the high V and Ag contents of the oxidized Ridenour ores thus almost certainly are due to secondary enrichment through oxidation. Oxidation at the Ridenour pipe has been so extensive that the primary ore minerals, such as uraninite, pyrite, chalcopyrite, bravoite, galena, and sphalerite, all of which are common in reduced ore from other pipes, have almost been totally removed from the Ridenour pipe. Only trace amounts of residual pyrite and galena have been observed. Supergene minerals, in approximate order of decreasing abundance, include malachite, azurite, goethite, hematite, roscoelite, tyuyamunite, metatyuyamunite, volborthite, calciovolborthlte, conichalcite, vesignieite, naummanite, and argentite. The high vanadium content of most of the rocks is due to the presence of roscoelite, which replaced the normal dolomitic cement in the sandstone matrix. The Ridenour pipe appears to be an oxidized version of the uranium-rich Orphan mine. The geochemistry and stratigraphic controls on the ore are identical. Extending the analogy, there appears to be little potential for an economic uranium orebody at the Ridenour mine because the ore zone in the Esplanade is oxidized, and the underlying Wescogame Formation at the Orphan mine did not yield much ore. In contrast, the average vanadium content at the 1 Ridenour mine is 10 times that of uranium, and hence, may have potential as an economic commodity.

Journal of Volcanology and Geothermal Research, May 1, 1979

Several high-temperature (950-1060 ° C) gas samples were collected with a new sampling device fro... more Several high-temperature (950-1060 ° C) gas samples were collected with a new sampling device from lava flows and a vent during the September 1977 Kilauea eruption. After removal of atmospheric contaminants (N2, At, 02) ' the gases are water-rich (90-95 mole %). This may be attributed to meteoric water or be indicative of relatively degassed, partially cooled magma that filled the rift zone. Numerous hydrocarbons in addition to CH 4 were present in a sample obtained in the presence of pyrolyzing vegetation.

New Mexico Mineral Symposium

Science, 1987

Shocked quartz grains displaying planar features were isolated from Cretaceous-Tertiary boundary ... more Shocked quartz grains displaying planar features were isolated from Cretaceous-Tertiary boundary clays at five sites in Europe, a core from the north-central Pacific Ocean, and a site in New Zealand. At all of these sites, the planar features in the shocked quartz can be indexed to rational crystallographic planes of the quartz lattice. The grains displaying streaking indicative of shock in X-ray diffraction photographs and also show reduced refractive indices. These characteristic features of shocked quartz at several sites worldwide confirm that an impact event at the Cretaceous-Tertiary boundary distributed ejecta products in an earth-girdling dust cloud, as postulated by the Alvarez impact hypothesis.

Physics and Chemistry of the Earth, 1975

To Investigate the proposal that kimberlites and associated rocks originate by anatexIs of mantle... more To Investigate the proposal that kimberlites and associated rocks originate by anatexIs of mantle pendotlte in a H 2 O-and COrrich environment, phase relationships offour peridotite (lherzolite) nodules and one websterite nodule were investigated to 12OD"C and 30 kbar in the presence of H 2 0 and H 2 O-C0 2 vapors with controlled oxygen fugacIty. Solidus temperatures, which are a function of vanous parameters including bulk composition, total pressure. and a H20 , are considerably (12D-2OD°e) lower than previous determinations. Melting of garnet lherzolIte, even in the presence of a vapor of 50/50 mol.~~H 2 0/C0 2 (XH;o = 0.5). begins at depths of less than 150 km beneath the continental shields. This Investigation was augmented by a study of the stabilIty of phlogopite in the system K 2 0-MgO-CaO-AI20rSIOrH20 to 35 kbar at PeH,O <1; P T and -PT' The reactIOn phlogopite + enstatite" + dlOpslde"~forsterite + pyrope + liquid occurs at about 1350°C at 35 kbar. These temperatures are considerably higher than those of the vapor-saturated solIdil of the peridotite nodules, reflecting the absence of Fe and Na and the very low values of aH2 0 ' In expenments with the nodules, phlogopite appeared only when the compositions were spiked with phlogopite. Amphiboles occurred in all experiments with the nodules at pressures below 20-25 kbar. These amphiboles become enriched in pargasite component relative to tschermakite component with increasIng pressure and decreasing temperature. Temperatures indIcated by the compositions of orthopyroxenes coexisting with clInopyroxenes are approximately IOD°C lower than those obtained from previously publIshed pyroxene geothermometers.

Physics and Chemistry of the Earth, 1975

To Investigate the proposal that kimberlites and associated rocks originate by anatexIs of mantle... more To Investigate the proposal that kimberlites and associated rocks originate by anatexIs of mantle pendotlte in a H 2 O-and COrrich environment, phase relationships offour peridotite (lherzolite) nodules and one websterite nodule were investigated to 12OD"C and 30 kbar in the presence of H 2 0 and H 2 O-C0 2 vapors with controlled oxygen fugacIty. Solidus temperatures, which are a function of vanous parameters including bulk composition, total pressure. and a H20 , are considerably (12D-2OD°e) lower than previous determinations. Melting of garnet lherzolIte, even in the presence of a vapor of 50/50 mol.~~H 2 0/C0 2 (XH;o = 0.5). begins at depths of less than 150 km beneath the continental shields. This Investigation was augmented by a study of the stabilIty of phlogopite in the system K 2 0-MgO-CaO-AI20rSIOrH20 to 35 kbar at PeH,O <1; P T and -PT' The reactIOn phlogopite + enstatite" + dlOpslde"~forsterite + pyrope + liquid occurs at about 1350°C at 35 kbar. These temperatures are considerably higher than those of the vapor-saturated solIdil of the peridotite nodules, reflecting the absence of Fe and Na and the very low values of aH2 0 ' In expenments with the nodules, phlogopite appeared only when the compositions were spiked with phlogopite. Amphiboles occurred in all experiments with the nodules at pressures below 20-25 kbar. These amphiboles become enriched in pargasite component relative to tschermakite component with increasIng pressure and decreasing temperature. Temperatures indIcated by the compositions of orthopyroxenes coexisting with clInopyroxenes are approximately IOD°C lower than those obtained from previously publIshed pyroxene geothermometers.

2002 New Mexico Mineral Symposium, Proceedings Volume

1980 New Mexico Mineral Symposium, Proceedings Volume

Open-file report /, 1994

American Journal of Science, May 1, 1973

Open-file report /, 1998

Open-file report /, 1986

Rocks and minerals, Aug 1, 2002

Physics and chemistry of the earth, 1975

Open-File Report, 1990

Journal of Volcanology and Geothermal Research, May 1, 1979

New Mexico Mineral Symposium

Science, 1987

Physics and Chemistry of the Earth, 1975

To Investigate the proposal that kimberlites and associated rocks originate by anatexIs of mantle... more To Investigate the proposal that kimberlites and associated rocks originate by anatexIs of mantle pendotlte in a H 2 O-and COrrich environment, phase relationships offour peridotite (lherzolite) nodules and one websterite nodule were investigated to 12OD"C and 30 kbar in the presence of H 2 0 and H 2 O-C0 2 vapors with controlled oxygen fugacIty. Solidus temperatures, which are a function of vanous parameters including bulk composition, total pressure. and a H20 , are considerably (12D-2OD°e) lower than previous determinations. Melting of garnet lherzolIte, even in the presence of a vapor of 50/50 mol.~~H 2 0/C0 2 (XH;o = 0.5). begins at depths of less than 150 km beneath the continental shields. This Investigation was augmented by a study of the stabilIty of phlogopite in the system K 2 0-MgO-CaO-AI20rSIOrH20 to 35 kbar at PeH,O <1; P T and -PT' The reactIOn phlogopite + enstatite" + dlOpslde"~forsterite + pyrope + liquid occurs at about 1350°C at 35 kbar. These temperatures are considerably higher than those of the vapor-saturated solIdil of the peridotite nodules, reflecting the absence of Fe and Na and the very low values of aH2 0 ' In expenments with the nodules, phlogopite appeared only when the compositions were spiked with phlogopite. Amphiboles occurred in all experiments with the nodules at pressures below 20-25 kbar. These amphiboles become enriched in pargasite component relative to tschermakite component with increasIng pressure and decreasing temperature. Temperatures indIcated by the compositions of orthopyroxenes coexisting with clInopyroxenes are approximately IOD°C lower than those obtained from previously publIshed pyroxene geothermometers.

Physics and Chemistry of the Earth, 1975

To Investigate the proposal that kimberlites and associated rocks originate by anatexIs of mantle... more To Investigate the proposal that kimberlites and associated rocks originate by anatexIs of mantle pendotlte in a H 2 O-and COrrich environment, phase relationships offour peridotite (lherzolite) nodules and one websterite nodule were investigated to 12OD"C and 30 kbar in the presence of H 2 0 and H 2 O-C0 2 vapors with controlled oxygen fugacIty. Solidus temperatures, which are a function of vanous parameters including bulk composition, total pressure. and a H20 , are considerably (12D-2OD°e) lower than previous determinations. Melting of garnet lherzolIte, even in the presence of a vapor of 50/50 mol.~~H 2 0/C0 2 (XH;o = 0.5). begins at depths of less than 150 km beneath the continental shields. This Investigation was augmented by a study of the stabilIty of phlogopite in the system K 2 0-MgO-CaO-AI20rSIOrH20 to 35 kbar at PeH,O <1; P T and -PT' The reactIOn phlogopite + enstatite" + dlOpslde"~forsterite + pyrope + liquid occurs at about 1350°C at 35 kbar. These temperatures are considerably higher than those of the vapor-saturated solIdil of the peridotite nodules, reflecting the absence of Fe and Na and the very low values of aH2 0 ' In expenments with the nodules, phlogopite appeared only when the compositions were spiked with phlogopite. Amphiboles occurred in all experiments with the nodules at pressures below 20-25 kbar. These amphiboles become enriched in pargasite component relative to tschermakite component with increasIng pressure and decreasing temperature. Temperatures indIcated by the compositions of orthopyroxenes coexisting with clInopyroxenes are approximately IOD°C lower than those obtained from previously publIshed pyroxene geothermometers.