Peter K. M. Megaw

Jiangxi Copper (China)

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Ryan Mathur

Juniata College

Antonio Arribas

The University of Texas at El Paso

Ken Robertson

Joaquín Ruiz

Universidad de Zaragoza

Michael R. Gray

Australian Museum

Isabel Arribas

Instituto Geológico y Minero de España

Tyler L. Spano

Oak Ridge National Laboratory

M. Gaft

Ariel University

Malcolm Southwood

University of Wollongong

Nicholas E. Pingitore

The University of Texas at El Paso

Cooperative Institutions

Juniata College

Centre National de la Recherche Scientifique

University of British Columbia

Nantes Université

The University of Texas at El Paso

University of Arizona

Institut des Matériaux Jean Rouxel

Gemological Institute of America

Newmont Mining (United States)

Universidad Politécnica de Madrid

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Connoisseur’s Choice: Malachite Pseudomorphs after Azurite—Part 2: Milpillas, Mexico and Other Worldwide Localities

Rocks & Minerals (2022)

Peter K. M. Megaw Evan A. Jones Bruce Cairncross Malcolm Southwood

Pseudomorph

Malachite

Malachite green

10.1080/00357529.2022.2087150

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Citations (1)

The Second China (Changsha) Mineral and Gem Show, 15–20 May 2014

Rocks & Minerals (2014)

Peter K. M. Megaw

Click to increase image sizeClick to decrease image size ACKNOWLEDGMENTSI was deeply honored to be welcomed back for the Second China (Changsha) Mineral and Gem Show and wish to again express my warm appreciation for Mr. Xiao's ambitious vision and hospitality. Dr. John Hou deserves special thanks for making Changsha such a pleasant repeat experience. His work with the volunteers was again nothing short of spectacular, and it was a blast getting to know Zoe, Kendra, Lauren, and Leo from this enthusiastic crew. Dr. Guanghua Liu is also thanked for his careful review of the locality attributions and a delightful dinner. Dr. Rob Lavinsky continues to provide support and advice to the show organizers and the Chinese collecting community in general. I also thank the (reduced) international contingent, especially Bryan Lees, Richard Jackson, Monica Kitt, Gene Meireran, Steve Smale, Andreas Massanek, George Stacey, and Allan Arnold for hospitality and companionship. Finally, my deepest thanks go to Cassie for her local knowledge, excellent translations, and ready smile (good luck on your exams!).Figure 20. Cabinet-sized group (20 cm) of emerald crystals from Malipo, Wenshan City, Yunnan Province, China, worked out of matrix.Display full sizeFigure 21. Purple octahedral fluorites with quartz coating partially removed. Nice to see the physical removal instead of chemical overcleaning with hydrofluoric acid.Display full sizeFigure 22. Purple cubic fluorites with prominent growth spirals on each cube face from Weishan, Yunnan Province, China—highly reminiscent of the material from El Filo mine, Mapimi, Durango, Mexico.Display full sizeFigure 23. Radiating group (25 cm) of white nailhead calcites from Nanyang City, Henan Province, China. A number of these were on offer, and this one found a home at the Rice Mineralogical Museum in Portland, Oregon.Display full sizeFigure 24. Large plate (35 cm) of new orange-red wulfenites leached out of massive calcite, unfortunately at the price of its luster, from Malan, Xinjiang Province, China.Display full sizeFigure 25. The Changsha Show has arrived—they had tailgaters on Saturday and Sunday afternoons!Display full sizeAdditional informationNotes on contributorsPeter MegawDr. Peter Megaw, a consulting editor of Rocks & Minerals, is a well-known geologist, mineral collector, author, and longtime exhibits chair for the Tucson Gem and Mineral Show.™

10.1080/00357529.2014.949169

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Volcanic Rocks of the Sierra Pastorias Caldera Area, Chihuahua, Mexico

American Association of Petroleum Geologists eBooks (1981)

Peter K. M. Megaw

This volume has been nurtured by the world's continuing concern for energy, and more specifically, mans' efforts to seek uranium resources in new geologic environments. Recent exploration research has emphasized a broad variety of geological environments for uranium, with a consistent effort to diversify the type of geologic target. Sandstone uranium environments have dominated the U.S. resource situation, whereas in many other countries such deposits play only a minor role. The majority of the 23 papers contained here were presentations at a symposium in 1980. These studies are neither summaries nor all-emcompasing reviews of their respective topics; rather, they are reports on results from recently completed or still evolving reserach or exploration projects.

Caldera

10.1306/st13421c17

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Citations (3)

Geology and Mineralogy of Electric Opal^TM: Green Daylight-Luminescing Hyalite Opal from Zacatecas, Mexico

Rocks & Minerals (2018)

Peter K. M. Megaw Emmanuel Fritsch Tyler L. Spano Michael R. Gray

In October 2013, five weathered specimens of botryoidal opal rough showing moderate green daylight luminescence were received from Ruben Avila (Gemimex), well-known El Paso-Juarez based importer of...

Daylight

10.1080/00357529.2018.1477007

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Systematic Variation in Galena Solid-Solution Compositions atSanta Eulalia, Chihuahua, Mexico

Economic Geology (2000)

V. W. Lueth Peter K. M. Megaw Nicholas E. Pingitore P. Goodell

Argentiferous galena is the main silver-bearing phase at both the East and West camps of the Santa Eulalia district, Chihuahua, Mexico. The silver occurs as a coupled substitution of Ag and Sb for Pb in PbS with compositions ranging from 0.04 to 5.9 atomic percent (at. %) Ag and 0.10 to 7.2 at. percent Sb. Correlation analysis between Ag and Sb resulted in r values of 0.97 and 0.99 (significant at the 98% confidence level) for direct-current plasma-atomic emission spectroscopy (DCP-AES) and microprobe analysis of galena, respectively. Discrete and crystallographically oriented inclusions of diaphorite (usually 1 μ m or smaller) were common in high silver-antimony galenas and rare in low silver types (when present, tend to be larger). These inclusions were most abundant in the core zones of the crystals and rare on the edges. Spatial and temporal variations in Ag-Sb concentrations and ratios in galena were found mainly in the West camp of the district. High silver galenas (maximum 5.9 at. %) are confined to skarn zones or deep manto and chimney areas. The Ag/Sb ratio increases in galena from depth (0.88) to the surface (1.04) and from south (0.76) to north (0.94), following zonation and flow patterns established in previous investigations. Differences in Ag-Sb substitution in galena are also seen in different mineralization types: breccia zones, deep mantos, and chimneys contain more Ag-Sb (3.5 at. % avg) and have lower Ag/Sb ratios (avg ratio = 0.88) than the upper mantos, silicate and calc-silicate orebodies, which have lower Ag-Sb concentrations (2.2 avg at. %) but higher ratios (avg ratio = 1.00). Silver and antimony substitution also correlates with sulfur isotope variation in the district. Within individual orebodies, the δ 34S value increases with decreasing silver and antimony concentrations in galena. The solid-solution compositional variations in galena coupled with sulfur isotope values are a useful tool for inferring fluid paths and appear to reflect fluid evolution. At Santa Eulalia, silver is disseminated to various degrees throughout the orebodies and galena solid-solution concentrations appear to be controlled by subtle physical and/or chemical gradients. This contrasts with volcanic-epithermal systems in which significant physiochemical perturbations (large thermal and pressure gradients, boiling, etc.) lead to dumping of precious metals and semimetals as sulfosalts in bonanza zones. Relatively low concentrations of other potential ore-forming elements, namely copper and bismuth, also precluded the formation of a complex suite of silver sulfosalts and antimonian-argentiferous galena precipitated instead. Sulfosalts at Santa Eulalia are localized to upper mineralized zones as breccia void fillings, indicative of limited zones of boiling.

Variation (astronomy)

10.2113/gsecongeo.95.8.1673

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Citations (35)

Use of Cu isotopes to distinguish primary and secondary Cu mineralization in the Cañariaco Norte porphyry copper deposit, Northern Peru

Mineralium Deposita (2012)

Ryan Mathur Joaquín Ruiz Michael J. Casselman Peter K. M. Megaw Robert van Egmond

Chalcocite

Hypogene

Covellite

Supergene (geology)

Bornite

Copper sulfide

10.1007/s00126-012-0439-y

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Citations (55)

Grand Opening of the New Mineral Museum at New Mexico Tech University, Socorro, New Mexico, 10 November 2015

Rocks & Minerals (2016)

Peter K. M. Megaw

Socorro, New Mexico, is a gem of a small college town nestled on the banks of the Rio Grande about 75 miles (120 kilometers) south of Albuquerque (fig. 4).Socorro lies on the eastern fringe of the ...

10.1080/00357529.2016.1138425

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Exploration on the Cinco de Mayo Carbonate Replacement Project, Chihuahua, Mexico

Ken Robertson Peter K. M. Megaw Jim McGlasson Dan MacInnis

The study, evaluation and interpretation of the Cinco de Mayo survey results is ongoing, however we will show that integrating geologic models with geophysical exploration methods applied over the last two years contributed to the discovery of significant massive sulphides late in 2007. The techniques applied include completion of an airborne TEM survey, 3D magnetic inversions, PEM and AMT survey results.

10.1190/1.3059123

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Tellurium oxysalts from Tombstone, Arizona

... New Mexico Mineral Symposium (2001)

Peter K. M. Megaw

The mention of the Tombstone district of southeastern Arizona conjures up romantic images of the old West including prospectors braving hostile Apaches to make the initial discovery, the Earp brothers and the "Shoot out at the OK Corral," and enough wealth pouring out of the mines to support a non-stop 24/7 poker game...with a $1,000 buy-in for 5 yrs!Of course the prospector sold out cheap and died penniless, the Earp brothers' reputation has tarnished with time, and the fabu¬lous ores played out long ago.Today, the Tombstone district is a world-renowned tourist trap, and the mines are largely inaccessible.However, the Tombstone district has produced a number of rare tellurium oxysalts, is type locality for nine such species, and a number of unknowns are awaiting description.Tombstone mining commenced about 1881 on high-grade ores that cropped out on the surface.These bonanza oxide ores were rapidly followed to the water table, about 150 m below the surface.Massive pumps were installed to allow following the rich underlying sulfide ores to depths ulti¬mately reaching over 350 m.The pumps were unable to hold back the water influx, and when one pump failed in the 1890s, the entire district flooded rapidly to the water table.One later attempt was made in 1912 to dewater the mines and pursue deep ores, but except for this, all twentieth century mining was focused on scavenging remnants and lower-grade ores bypassed in the rush to follow bonanzas to depth.Total district production is estimated to be 2,700,000 tons, grading: 1.53 grams per ton Au; 372 grams per ton Ag; 0.8% Pb; 0.02% Zn; and 0.13% Cu (Titley, 1993).These are average grade figures and do not begin to reflect the extremely high gold and silver grades found in the enriched upper parts of the system.

Tellurium

10.58799/nmms-2001.246

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Connoisseur's Choice: Distinctive Twinned Calcite from the Palmarejo Mine, Chihuahua, Mexico

Rocks & Minerals (2018)

Peter K. M. Megaw Terry E. Huizing R. Peter Richards Jeffrey E. Post

Calcite comes from such a seemingly infinite number of worldwide localities and shows such a bewilderingly wide range of colors and associations, forms, and habits, including twins, that new finds ...

10.1080/00357529.2018.1477010

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