Geology topics

Mark D. Barton

Publications and source records attributed to Mark D. Barton.

4 recordsLinked to original sources

USGS2014

Succession of Laramide magmatic and magmatic-hydrothermal events in the Patagonia Mountains, Santa Cruz County, Arizona

This investigation of the space-time progression of magmatism and hydrothermal activity in the Patagonia Mountains of southern Arizona is based on field and paragenetic relationships, and on U-Pb and 40 Ar/ 39 Ar geochronology of igneous and hydrothermal minerals. The Patagonia Mountains consist of Precambrian, Paleozoic, and Mesozoic sedimentary, granitic, and volcanic rocks, Laramide volcanic rocks, and a core of Laramide intrusions that comprise the Patagonia Mountains batholith. Laramide igneous rocks and adjacent Paleozoic and Mesozoic rocks contain significant porphyry Cu-Mo deposits, Mo-Cu breccia pipes, Ag replacement deposits, and numerous other Cu-Pb-Zn-Ag replacement and vein deposits. Ages of igneous and hydrothermal minerals from 20 U-Pb and 52 40 Ar/ 39 Ar determinations define four magmatic and magmatic-hydrothermal events that formed the batholith and altered parts of it and adjacent rocks; cumulatively the events span at least 16 m.y., from ~74 to 58 Ma. The oldest event of this succession includes the 74 Ma Washington Camp stock and spatially associated Cu-Pb-Zn-Ag replacement deposits in Paleozoic carbonate rocks of the Washington Camp-Duquesne district. Eruption of 73 to 68 Ma volcanic rocks in the northern part of the range was the next youngest event, which coincides temporally with replacement and vein deposits in Paleozoic carbonate rocks at the Flux mine (~71 Ma). An event at 65 to 62 Ma is marked by emplacement of small-volume quartz monzonite, granodiorite, and diorite intrusions, formation of the Ventura breccia deposit in Jurassic granite at 65 to 64 Ma, and formation of other Pb-Zn-Ag-Cu replacement and vein deposits (~62 Ma; Blue Nose and Morning Glory). The Red Mountain porphyry Cu-Mo system is hosted by ~62 Ma granodiorite and Laramide volcanic rocks (73–68 Ma) at the northern end of the batholith. It includes a deep, chalcopyrite-bornite resource (~60 Ma) that is associated with potassic and sericitic alteration and a near-surface chalcocite-enargite resource (60 Ma) that is associated with advanced, supergene-enriched argillic alteration. The youngest event includes the Sunnyside porphyry Cu-Mo system and a Cu-Mo breccia deposit at Red Hill (Four Metals mine), both of which formed in large-volume quartz monzonite, granodiorite, quartz monzonite porphyry, and quartz feldspar porphyry (~61–59 Ma). Similar to the Red Mountain system, the Sunnyside system consists of a deep chalcopyrite resource that occurs in ~60 to 59 Ma quartz feldspar porphyry, and a near-surface, slightly younger (~59–58 Ma) enargite-chalcocite-tennantite resource that occurs in quartz feldspar porphyry, quartz monzonite porphyry, and Mesozoic rocks. The Red Hill Cu-Mo breccia deposit is hosted by large-volume quartz monzonite, granodiorite, and quartz monzonite porphyry (~61–59 Ma). Discrepancies between field and paragenetic relationships and some analytic ages at Sunnyside and Red Hill preclude precise dating of mineralization stages, and may reflect disturbance of isotope systems by multiple, co-spatial to juxtaposed intrusive and hydrothermal events, and/or by unrecognized intrusions. Numerous vein and replacement deposits at the northern end of the batholith, including the Hardshell Ag resource and the Three R supergene chalcocite resource, are distal deposits of the Sunnyside and Red Mountain systems. Small, ~61 to 59 Ma Cu-Mo deposits in large-volume intrusions in the southern part of the batholith consist of hydrothermal quartz, biotite, K-feldspar, muscovite, chalcopyrite, and molybdenite. The age span of magmatic and magmatic-hydrothermal events in the Patagonia Mountains, minimally 16 m.y., is comparable to that of certain other magmatic-hydrothermal successions that contain porphyry Cu-Mo systems. Magmatic-hydrothermal events of the Wasatch-Oquirrh igneous trend, Utah, and the Boulder batholith, Montana, both span ~17 m.y. and include the Bingham and Butte porphyry Cu-Mo, vein and replacement deposits, respectively. Plutons and mineral deposits in the Pima district, Arizona, which includes the porphyry Cu-Mo deposits at Sierrita-Esperanza, Mission-Pima-San Xavier North, and Twin Buttes, formed over an interval of ~14 m.y. The diversity of igneous and hydrothermal products likely reflects evolutionary processes occurring at multiple sites in the lithosphere and at different time scales from >10 m.y. to less than the geochronologic precision currently achievable.

Arizona↗

USGS2010

Porphyry copper deposit model

This report contains a revised descriptive model of porphyry copper deposits (PCDs), the world's largest source (about 60 percent) and resource (about 65 percent) of copper and a major source of molybdenum, gold and silver. Despite relatively low grades (average 0.44 percent copper in 2008), PCDs have significant economic and societal impacts due to their large size (commonly hundreds of millions to billions of metric tons), long mine lives (decades), and high production rates (billions of kilograms of copper per year). The revised model describes the geotectonic setting of PCDs, and provides extensive regional- to deposit-scale descriptions and illustrations of geological, geochemical, geophysical, and geoenvironmental characteristics. Current genetic theories are reviewed and evaluated, knowledge gaps are identified, and a variety of exploration and assessment guides are presented. A summary is included for users seeking overviews of specific topics.

Scientific Investigations Report↗

USGS1995

Porphyry copper and other intrusion-related mineralization in Mexico

Intrusion-related copper-bearing ore deposits in Mexico span a wide-range of deposit types and geological settings and formed from the mid-Mesozoic through the Holocene. These deposits include world-class copper porphyry and skarn deposits as well as a continuum of similar skarn, porphyry, vein, and replacement deposits that contain variable quantities of molybdenum, zinc, silver, lead, iron, gold, tungsten, tin, fluorine, and beryllium. Based on a new compilation, this paper reviews data on the full spectrum of intrusion-related deposits, concentrating on copper-rich systems, and attempts to place them in a generalized geological and petrological context. In Mexico, intrusion-related mineral deposits are primarily Mesozoic to middle Tertiary in age. Three broad periods are prominent in the mineralization record: the late Mesozoic, the Laramide, and the middle Tertiary. Jurassic to Late Cretaceous calc-alkalic batholiths with sparse volcanic rocks occur along the Pacific margin mainly on eugeoclinal crust, although locally on continental crust (for example, in Sonora). Latest Cretaceous to Early Tertiary ('Laramide') calc-alkalic batholithic, subvolcanic, and volcanic centers occur in an overlapping but somewhat more easterly band that extends with diminished intensity and somewhat younger ages into the Sierra Madre Oriental. Mid-Tertiary volcanism and local intrusive centers are widely developed, with the greatest abundance of calcalkalic felsic volcanics in the Sierra Madre Occidental and more mafic middle to late Tertiary arc volcanics in the Sierra Madre del Sur in southern Mexico and as a fringe of alkalic volcanic' and sub volcanic centers in northeastern Mexico. Over 600 copper-rich intrusion-related systems can be inferred from the literature; about 100 can be documented with some confidence. Copper-rich deposits occur with both intermediate (dioritic) and felsic (granodioritic) intrusive centers and show a corresponding variety of associated metals and alteration types. Styles include porphyry-type disseminated or stockwork mineralization, skarn, breccia pipes, and pegmatites. Multiple styles commonly occur in the same district. Porphyry copper deposits are best developed in association with the Laramide intrusive centers of northern Mexico and the mid-Tertiary intrusions in southern Mexico. Other intrusion-related deposit types occur within the same magmatic framework, but they have different temporal and spatial correlations related to their igneous composition and exposure level. The continuum of intrusion-related mineralization in Mexico can be divided by geological associations, metal contents, and styles of alteration. Although more than 1,500 intrusion-associated mineral deposits are known, the scarcity of data requires a simplified approach focusing on major districts. We distinguish the following overlapping groups of deposits based on their metal contents and igneous compositions: (1) porphyry or skarn Cu(-Mo-Zn) associated with intermediate to felsic granitoids, (2) porphyry or skarn Cu (-Au-Fe) associated with intermediate intrusions, (3) greisen, skarn, or pegmatite W(-Mo) associated with intermediate to felsic granitoids, (4) replacement or skarn Zn-Pb-Ag(-Cu-F) deposits associated with felsic intrusions, (5) volcanic-hosted vein Ag-Au(-Zn-F-Sn) deposits associated with hypabyssal felsic intrusions, (6) vein ± replacement Ag-Au(-Cu-Zn-Pb) deposits associated with intermediate stocks, (7) volcanichosted Au-Ag(-Cu) systems, (8) rhyolite-related F(-Sn-Be) deposits, (9) diorite-related Fe(-Au-Cu) skarns, and (9) rhyolite-related Fe deposits. Some inferences can be drawn from examination of these patterns: • Igneous compositions vary in time and space in Mexico, but multiple compositions commonly were emplaced at different times in the same region. Temporal variations (as in Sonora) are as important as differences in province (as between Sonora and southern Mexico). • Alteration and metal differences between alkaline and sub alkaline, felsic and mafic magma suites can be partly rationalized from equilibria among igneous minerals (for example, in terms of a Al 2 O 3 vs a CaO [vs a SiO 2 ]), fluid chloride and sulfur contents, and magmatic metal contents which reflect province and process. • Exposure and preservation filter observed Mexican metallogeny. Erosion of the Mesozoic arc superstructure in the west leaves mainly tungsten-skarns, burial of the Laramide arc in central Mexico interrupts porphyry copper patterns, and minimal exhumation of mid-Tertiary intrusive centers preserves distal vein or replacement systems. • The superimposed metallogenic patterns in Mexico have parallels with metallogenic patterns in the western United States in terms of the effects of preservation, process, and province. Future work should focus on increasing the basic geological data on mineral deposits and igneous rocks. Geochronology, petrology, and geochemistry would help better define the temporal, spatial, and compositional interrelationships between tectonism, magmatism, and mineralization.

Book chapter↗

USGS1987

Heat capacity and thermodynamic properties of andradite garnet, Ca 3 Fe 2 Si 3 O 12 , between 10 and 1000 K and revised values for ΔfGom (298.15 K) of hedenbergite and wollastonite

The heat capacity of synthetic andradite garnet (Ca 3 Fe 2 Si 3 O 12 ) was measured between 9.6 and 365.5 K by cryogenic adiabatic calorimetry and from 340 to 990 K by differential scanning calorimetry. At 298.15 K C o p , m and S o m are 351.9 ± 0.7 and 316.4 ± 2.0 J/(mol·K), respectively. Andradite has a λ-peak in C o p , m with a maximum at 11.7 ± 0.2 K which is presumably associated with the antiferromagnetic ordering of the magnetic moments of the Fe 3+ ions. The Gibbs free energy of formation, Δ f G o m (298.15 K) of andradite is −5414.8 ± 5.5 kJ/mol and was obtained by combining our entropy and heat capacity data with the known breakdown of andradite to pseudowollastonite and hematite at ≈ 1410 to 1438 K. From a reexamination of the calcite + quartz = wollastonite equilibrium data we obtained Δ f H o m (298.15 K) = − 1634.5 ± 1.8 kJ/mol for wollastonite. Between 300 and 1000 K the molar heat capacity of andradite can be represented by the equation C o p , m = 809.24 - 7.025 × 10−2 T − 7.403 × 10 3 T −0.5 − 6.789 × 10 5 T −2. We have also used our thermochemical data for andradite to estimate the Gibbs free energy of formation of hedenbergite (CaFeSi 2 O 6 ) for which we obtained Δ f G o m (298.15 K ) = −2674.3 ± 5.8 kJ/mol.

Geochimica et Cosmochimica Acta↗