Abstracts concerning the geology of Hillsboro district, New Mexico
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McLemore, V. T., Munroe, E. A., Heizler, M. T. and McKee, C., 1999, Geochemistry of the Copper Flat porphyry and associated deposits in the Hillsboro mining district, Sierra County, New Mexico, USA: Journal of Geochemical Exploration, v. 66, p. 167-189.
ABSTRACT
New geochemical, geochronological, and geological data, combined with earlier studies, have provided a refinement of the evolution of mineralization in the Hillsboro district in central New Mexico. Laramide (polymetallic) vein, placer gold, carbonate-hosted Ag-Mn and Pb-Zn, and porphyry-copper deposits are found in this district. The Hillsboro district is dominated by Cretaceous andesite flows (75.4±3.5 Ma), breccias, and volcaniclastic rocks that were erupted from a volcano. The mineralized Copper Flat quartz-monzonite porphyry (CFQM, 74.93±0.66 Ma) intruded the vent of the volcano. The unmineralized Warm Springs quartz monzonite (74.4±2.6 Ma) and a third altered, unmineralized quartz monzonite intruded along fracture zones on the flanks of the volcano. Younger latite and quartz latite dikes intruded the andesite and CFQM and radiate outwards from the CFQM; the polymetallic vein deposits are associated with these dikes. The igneous rocks are part of a differentiated comagmatic suite. Alteration of the igneous rocks consists of locally intense silicification, biotite, potassic, phyllic, and argillic alteration. Large jasperoid bodies have replaced the El Paso Formation, Fusselman Dolomite, Lake Valley Limestone, and Percha Shale in the southern part of the district. Many workers in the district have recognized district zoning. The low sulfur (<7%) porphyry-copper deposit forms the center. Trending radially from the CFQM are Laramide Au-Ag-Cu veins. Carbonate-hosted replacement deposits (Ag, Pb, Mn, V, Mo, Zn) are located in the southern and northern parts of the district, distal from the center. Collectively, the evidence suggests that the deposits found in the Hillsboro district were formed by multiple convective hydrothermal systems related to the Copper Flat volcanic/intrusive complex.
KEYWORDS: Porphyry-copper deposit, New Mexico, polymetallic veins
Munroe, E. A., McLemore, V. T., and Dunbar, N. W., 2000, Mine waste rock pile geochemistry and mineralogy in southwestern New Mexico, USA; in ICARD 2000-Program from the 5th international conference on acid rock drainage: Society for Mining, Metallurgy, and Exploration, Inc., Littleton, Colo., pp. 58.
Munroe, E. A., McLemore, V. T., and Dunbar, N. W., 2000, Mine waste rock pile geochemistry and mineralogy in southwestern New Mexico, USA; in ICARD 2000-Proceedings from the 5th international conference on acid rock drainage: Society for Mining, Metallurgy, and Exploration, Inc., Littleton, Colo., pp. 1327-1336.
ABSTRACT
In New Mexico, there are at least 100,000 abandoned mine waste rock piles with widely ranging geochemical and mineralogical compositions. A geochemical and mineralogical study was implemented for five waste rock piles, some which contained sulfides, in the Hillsboro Mining District. Chemical and physical characteristics of mineral grains and their secondary mineral oxidation rinds were examined with the electron microprobe. Pyrite and chalcopyrite appear to be the most reactive to oxidizing conditions. Clays, iron oxide, iron hydroxide, iron sulfate, and primary texture rinds exist in the waste rock piles analyzed.
McLemore, V. T., Munroe, E. A., Heizler, M. T. and McKee, C., 2000, Geology and evolution of the Copper Flat Porphyry Copper system, Hillsboro mining district, Sierra County, New Mexico; in Geology and Ore Deposits 2000, The Great Basin and Beyond: Geological Society of Nevada, Program with abstracts, p. 63.
McLemore, V. T., Munroe, E. A., Heizler, M. T. and McKee, C., 2000, Geology and evolution of the Copper Flat Porphyry-Copper and associated mineral deposits in the Hillsboro mining district, Sierra County, New Mexico; in Cluer, J. K., Price, J. G., Struhsacker, E. M., Hardyman, R. F. and Morris, C. L. eds., Geology and Ore Deposits 2000, The Great Basin and Beyond: Geological Society of Nevada, Symposium Proceedings, in press.
ABSTRACT
Unlike many porphyry copper deposits in southwestern United States, the Hillsboro district, in central New Mexico, is well exposed, with minimal erosion, and offers an excellent opportunity to examine a relatively intact magmatic-hydrothermal system with multiple zones of different mineral deposit types. New geochemical, geochronological, and geological data, combined with earlier published studies, have provided a refinement of the evolution of mineralization in the district. Past production has been predominantly from the polymetallic veins and placer gold deposits, although minor production has occurred from the porphyry copper and carbonate-hosted Pb-Zn and Ag-Mn replacement deposits. The geology of the Hillsboro district is dominated by Cretaceous andesite flows (75.4±3.5 Ma, 40Ar/39Ar), breccias, and volcaniclastic rocks that were erupted from a volcano. The Copper Flat quartz monzonite porphyry stock (CFQM, 74.93±0.66 Ma, 40Ar/39Ar) intruded the vent of the volcano and hosts porphyry copper mineralization. The unmineralized Warm Springs quartz monzonite (74.4±2.6 Ma, 40Ar/39Ar) and a third altered, but unmineralized quartz monzonite intruded along fracture zones on the flanks of the volcano. Younger latite and quartz latite dikes intruded the andesite and CFQM and radiate outwards from the CFQM. Hydrothermal alteration of the igneous rocks consists of locally intense biotite-potassic, potassic, sericitic, propylitic, and argillic alteration. Large jasperoid bodies, as well as smaller masses of skarn and marble, replaced limestones in the southern part of the district. The porphyry copper deposit is characterized by low-grade hypogene mineralization that is concentrated within a breccia pipe in the CQFM stock. Polymetallic veins hosted by many of the latite/quartz latite dikes trend outward radially from the Copper Flat porphyry copper deposit. Carbonate-hosted replacement deposits (Ag, Pb, Mn, V, Mo, Zn) are found in the southern and northern parts of the district, distal to the Copper Flat porphyry copper deposit. Collectively, the evidence suggests that the mineral deposits found in the Hillsboro district were formed by large, convective magmatic-hydrothermal systems related to the Copper Flat volcanic/intrusive complex. The Copper Flat porphyry copper deposit exhibits very little supergene alteration and enrichment, in contrast to the extensive supergene alteration and enrichment at the Santa Rita and Tyrone, New Mexico and Morenci, Arizona porphyry copper deposits. This may be a result of a lower pyrite content (<2%) at Copper Flat, thereby preventing the supergene enrichment process from occurring. Another explanation for this difference is that the Copper Flat porphyry copper deposit remained buried in the subsurface until uplift at about 21-22 Ma (Kelley and Chapin, 1997), whereas the Santa Rita, Tyrone, and Morenci deposits were exposed to multiple periods of surface erosion, alteration, and supergene enrichments.
KEYWORDS: porphyry copper deposit, Laramide, Hillsboro, Copper Flat, vein deposits, New Mexico