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1-7 Wilt, Jan C., 1995, Correspondence of alkalinity and ferric/ferrous ratios of igneous rocks associated with various types of porphyry copper deposits, in Pierce, F. W., and Bolm, J. G., editors, Porphyry copper deposits of the American Cordillera: Arizona Geological Society Digest, v. 20, p. 180-200.
1-7 Wilt, Jan C., 1995, Correspondence of alkalinity and ferric/ferrous ratios of igneous rocks associated with various types of porphyry copper deposits, in Pierce, F. W., and Bolm, J. G., editors, Porphyry copper deposits of the American Cordillera: Arizona Geological Society Digest, v. 20, p. 180-200.
ABSTRACT
The MagmaChem classification and neural networks, a new type of pattern recognition software, have promising applications to mineral exploration and to alteration and zoning studies and have profound implications to metallogenesis. Part of the MagmaChem classification was evaluated by assigning 43 deposits to six subclasses defined on eight variation diagrams, training neural networks to classify analyses of 205 igneous and 887 mineralized samples, and testing the networks on their ability to classify new data.
Porphyry copper deposits are characteristic of six different alkalinity and ferric/ferrous ratio categories in the MagmaChem classification. Porphyry copper deposits occur in calcic weakly oxidized, calc-alkalic oxidized, calc-alkalic weakly oxidized, quartz alkalic oxidized, quartz alkalic weakly oxidized, and nepheline alkalic oxidized subclasses. Calcic weakly oxidized deposits include Panguna, Yandera, Koloula, Ertzberg, and Plesyumi. Calc-alkalic weakly oxidized deposits include Ajo, Dexing, El Salvador, FriedaRiver, Morenci, Potrerillos, CopperCanyon, and Hedley. Calc-alkalic oxidized deposits include Bagdad, Christmas, Lakeshore, Miami-Inspiration, Ray, Mineral Park, San Manuel, Sierrita-Esperanza, Silver Bell, Twin Buttes-Mission, Valley Copper, Tyrone, Cerro Colorado, Yerington, Cananea, and Chuquicamata. Calc-alkalic oxidized deposits include world class deposits that have the best grade and tonnage characteristics of all porphyry copper deposits. Examples of quartz alkalic weakly oxidized deposits include Bingham and Carr Fork, Copper Flat-Hillsboro, Copper Mountain, Bajo de la Alumbrera, Ok Tedi, Robinson (Ely), and Ingerbelle. Quartz alkalic oxidized deposits include Bisbee and Cerrillos. Nepheline alkalic weakly oxidized to oxidized deposits include Caribou-Bell and Galore Creek.
Of the six porphyry copper in the MagmaChem classification, only two were studied in detail; these were compared to four other deposit types of different alkalinity and oxidation character. Whole rock oxides of fresh igneous rocks were correlated with trace elements in rock chip samples from temporally and spatially associated ore deposits of six alkalinity and oxidation subclasses. The K2O versus SiO2 diagram best defined the alkalinity classes of calc-alkalic and alkali-calcic; the Fe2O3/FeO versus SiO2 diagram and iron mineralogy best defined oxidation subclasses of oxidized, weakly oxidized, and reduced. SiO2/K2O ratios of alkali-calcic igneous rocks range between 14 and 20 and those of calc-alkalic rocks are between 20 and 30. Fe2O3/FeO ratios are more than 0.8 with abundant magnetite and sphene for oxidized subclasses; between 0.5-1.2 with magnetite, sphene, and rare ilmenite for weakly oxidized subclasses; and less than 0.6 with only ilmenite in reduced subclasses.
Whole rock analyses from fresh igneous rocks were obtained from mining districts in which trace element geochemistry was also available. Lead-zinc-silver deposits such as Tombstone, Tintic, and ParkCity are related to oxidized alkali-calcic igneous rocks. Polymetallic lead-zinc-copper-tin-silver deposits such as Santa Eulalia, Railroad, Taylor, and Tempiute are associated with weakly oxidized alkali-calcic igneous rocks. Tin-silver deposits of Llallagua and Potosi are correlated with reduced alkali-calcic intrusives. Porphyry copper deposits such as Ray, Christmas, MineralPark, Highland Valley Copper, and Sierrita are derived from oxidized calc-alkalic plutons. Gold-rich porphyry copper deposits such as CopperCanyon, Ajo, El Salvador, El Teniente, Hedley, and Morenci are linked to weakly oxidized calc-alkalic plutons. Disseminated gold deposits such as Chimney Creek, Getchell, Carlin, and Northumberland are temporally and geochemically correlated with reduced calc-alkalic igneous rocks, although physical connections between plutons and Carlin-type deposits are rarely obvious.
Learning vector quantization and back-propagation artificial neural networks correctly classified 100 percent of igneous samples and 99 percent of mineralized samples. Discriminant analysis correctly classified only 96 and 83 percent of such samples. Neural networks trained with 90, 80, 70, or 50 percent of the samples correctly classified 81 to 100 percent of the randomly withheld samples. The high degree of correspondence between chemistries of igneous rocks and related mineralization implies genetic links between magmatic processes or sources and the ore deposits studied.
Key words
1-7 Wilt, Jan C., 1995, Correspondence of alkalinity and ferric/ferrous ratios of igneous rocks associated with various types of porphyry copper deposits, in Pierce, F. W., and Bolm, J. G., editors, Porphyry copper deposits of the American Cordillera: Arizona Geological Society Digest, v. 20, p. 180-200.
ABSTRACT
The MagmaChem classification and neural networks, a new type of pattern recognition software, have promising applications to mineral exploration and to alteration and zoning studies and have profound implications to metallogenesis. Part of the MagmaChem classification was evaluated by assigning 43 deposits to six subclasses defined on eight variation diagrams, training neural networks to classify analyses of 205 igneous and 887 mineralized samples, and testing the networks on their ability to classify new data.
Porphyry copper deposits are characteristic of six different alkalinity and ferric/ferrous ratio categories in the MagmaChem classification. Porphyry copper deposits occur in calcic weakly oxidized, calc-alkalic oxidized, calc-alkalic weakly oxidized, quartz alkalic oxidized, quartz alkalic weakly oxidized, and nepheline alkalic oxidized subclasses. Calcic weakly oxidized deposits include Panguna, Yandera, Koloula, Ertzberg, and Plesyumi. Calc-alkalic weakly oxidized deposits include Ajo, Dexing, El Salvador, FriedaRiver, Morenci, Potrerillos, CopperCanyon, and Hedley. Calc-alkalic oxidized deposits include Bagdad, Christmas, Lakeshore, Miami-Inspiration, Ray, Mineral Park, San Manuel, Sierrita-Esperanza, Silver Bell, Twin Buttes-Mission, Valley Copper, Tyrone, Cerro Colorado, Yerington, Cananea, and Chuquicamata. Calc-alkalic oxidized deposits include world class deposits that have the best grade and tonnage characteristics of all porphyry copper deposits. Examples of quartz alkalic weakly oxidized deposits include Bingham and Carr Fork, Copper Flat-Hillsboro, Copper Mountain, Bajo de la Alumbrera, Ok Tedi, Robinson (Ely), and Ingerbelle. Quartz alkalic oxidized deposits include Bisbee and Cerrillos. Nepheline alkalic weakly oxidized to oxidized deposits include Caribou-Bell and Galore Creek.
Of the six porphyry copper in the MagmaChem classification, only two were studied in detail; these were compared to four other deposit types of different alkalinity and oxidation character. Whole rock oxides of fresh igneous rocks were correlated with trace elements in rock chip samples from temporally and spatially associated ore deposits of six alkalinity and oxidation subclasses. The K2O versus SiO2 diagram best defined the alkalinity classes of calc-alkalic and alkali-calcic; the Fe2O3/FeO versus SiO2 diagram and iron mineralogy best defined oxidation subclasses of oxidized, weakly oxidized, and reduced. SiO2/K2O ratios of alkali-calcic igneous rocks range between 14 and 20 and those of calc-alkalic rocks are between 20 and 30. Fe2O3/FeO ratios are more than 0.8 with abundant magnetite and sphene for oxidized subclasses; between 0.5-1.2 with magnetite, sphene, and rare ilmenite for weakly oxidized subclasses; and less than 0.6 with only ilmenite in reduced subclasses.
Whole rock analyses from fresh igneous rocks were obtained from mining districts in which trace element geochemistry was also available. Lead-zinc-silver deposits such as Tombstone, Tintic, and ParkCity are related to oxidized alkali-calcic igneous rocks. Polymetallic lead-zinc-copper-tin-silver deposits such as Santa Eulalia, Railroad, Taylor, and Tempiute are associated with weakly oxidized alkali-calcic igneous rocks. Tin-silver deposits of Llallagua and Potosi are correlated with reduced alkali-calcic intrusives. Porphyry copper deposits such as Ray, Christmas, MineralPark, Highland Valley Copper, and Sierrita are derived from oxidized calc-alkalic plutons. Gold-rich porphyry copper deposits such as CopperCanyon, Ajo, El Salvador, El Teniente, Hedley, and Morenci are linked to weakly oxidized calc-alkalic plutons. Disseminated gold deposits such as Chimney Creek, Getchell, Carlin, and Northumberland are temporally and geochemically correlated with reduced calc-alkalic igneous rocks, although physical connections between plutons and Carlin-type deposits are rarely obvious.
Learning vector quantization and back-propagation artificial neural networks correctly classified 100 percent of igneous samples and 99 percent of mineralized samples. Discriminant analysis correctly classified only 96 and 83 percent of such samples. Neural networks trained with 90, 80, 70, or 50 percent of the samples correctly classified 81 to 100 percent of the randomly withheld samples. The high degree of correspondence between chemistries of igneous rocks and related mineralization implies genetic links between magmatic processes or sources and the ore deposits studied.
Key words
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