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1-9 Keith, S. B., Laux, D. P., Maughan, G., Schwab, K., Ruff, S., Swan, M. M., Abbott, E. W., and Friberg, S., 1991, Magma series and metallogeny; a case study from Nevada and environs, in Buffa, Ruth H., and Coyner, Alan R., editors, Geology and ore deposits of the Great Basin; field trip guidebook compendium: Geologic Society of Nevada, Reno, NV, p.404-493.
1-9 Keith, S. B., Laux, D. P., Maughan, G., Schwab, K., Ruff, S., Swan, M. M., Abbott, E. W., and Friberg, S., 1991, Magma series and metallogeny; a case study from Nevada and environs, in Buffa, Ruth H., and Coyner, Alan R., editors, Geology and ore deposits of the Great Basin; field trip guidebook compendium: Geologic Society of Nevada, Reno, NV, p.404-493.
ABS
The state of Nevada is one of the most metallized areas on earth. More than 90% of Nevada’s mineral districts are associated with Cordilleran arc magmatism of Triassic through recent age. Of particular significance is the overall heterogeneity of this metallogeny. Within any given mountain range as many as 10 distinct mineral systems may be present in a limited geographic area (the southern Toquima’s and northern Shoshone Mountains are two excellent examples that will be visited or seen on this field trip). These systems are too metallogenically distinct to have simply been derived from the host-rocks they have been emplaced into.
As heterogeneous as Nevada’s metallogeny is, the Mesozoic-Cenozoic magmatism is even more diverse. Nevada’s Mesozoic-Cenozoic history is mainly a record of wandering, hydrous, porphyritic magmatic arcs (metallogenic) produced by variable dip subduction and dry magmatism (non-metallogenic) produced by extensional tectonics (mainly the post-8 Ma Basin-Range extensional episode). As a result, the Mesozoic Cenozoic magma legacy is as complex as the metallogeny–especially the magma petrochemistry.
When considered in detail, however, a remarkably consistent empirical correlation between magma chemistry and metallogeny becomes apparent. It is the main purpose of this trip to show “ad nauseam” just how consistent this correlation is. Various spatial and temporal correlations between petrochemistry of associated magmatism, age, and metal chemistry of associated mineral districts are alluded to in the roadlogs. Summary comments as to the age, magma chemistry, and metal contents of the various mineral districts are presented in the commentary below. Special emphasis is placed on examples that will be visited in the field trip stops. Because gold metallogeny is most consistently associated with magmatism of hydrous calc-alkalicmetaluminous magma series affinity in Nevada, the field trip stops will examine mainly metallogeny associated with magmatism of demonstrable or strongly inferable calc-alkalic magma series affinity.
Within the porphyritic metaluminouscalc-alkalic (MCA) magma series, specialized subsets of metallogenycan be correlated with the oxidation state of the associated magmatism. Base metal (mainly Cu) expression empirically tracks oxidized calc-alkalic magmatism whereas Au-As metallogeny follows reduced calc-alkalic magmatism. Hence, the changes in metal specialization of porphyriticcalc-alkalic magma series as a function of both magma and crustal oxidation state is a major subtheme embedded within this text and accompanying roadlogs. At the end of this field trip, we hope to make a solid prima facie case that deposits in the Carlin Camp (Gold Strike in particular) are nothing more and nothing less than gold porphyries in the identical orthomagmatic sense that Yerington is a copper porphyry.
Key words
1-9 Keith, S. B., Laux, D. P., Maughan, G., Schwab, K., Ruff, S., Swan, M. M., Abbott, E. W., and Friberg, S., 1991, Magma series and metallogeny; a case study from Nevada and environs, in Buffa, Ruth H., and Coyner, Alan R., editors, Geology and ore deposits of the Great Basin; field trip guidebook compendium: Geologic Society of Nevada, Reno, NV, p.404-493.
ABS
The state of Nevada is one of the most metallized areas on earth. More than 90% of Nevada’s mineral districts are associated with Cordilleran arc magmatism of Triassic through recent age. Of particular significance is the overall heterogeneity of this metallogeny. Within any given mountain range as many as 10 distinct mineral systems may be present in a limited geographic area (the southern Toquima’s and northern Shoshone Mountains are two excellent examples that will be visited or seen on this field trip). These systems are too metallogenically distinct to have simply been derived from the host-rocks they have been emplaced into.
As heterogeneous as Nevada’s metallogeny is, the Mesozoic-Cenozoic magmatism is even more diverse. Nevada’s Mesozoic-Cenozoic history is mainly a record of wandering, hydrous, porphyritic magmatic arcs (metallogenic) produced by variable dip subduction and dry magmatism (non-metallogenic) produced by extensional tectonics (mainly the post-8 Ma Basin-Range extensional episode). As a result, the Mesozoic Cenozoic magma legacy is as complex as the metallogeny–especially the magma petrochemistry.
When considered in detail, however, a remarkably consistent empirical correlation between magma chemistry and metallogeny becomes apparent. It is the main purpose of this trip to show “ad nauseam” just how consistent this correlation is. Various spatial and temporal correlations between petrochemistry of associated magmatism, age, and metal chemistry of associated mineral districts are alluded to in the roadlogs. Summary comments as to the age, magma chemistry, and metal contents of the various mineral districts are presented in the commentary below. Special emphasis is placed on examples that will be visited in the field trip stops. Because gold metallogeny is most consistently associated with magmatism of hydrous calc-alkalicmetaluminous magma series affinity in Nevada, the field trip stops will examine mainly metallogeny associated with magmatism of demonstrable or strongly inferable calc-alkalic magma series affinity.
Within the porphyritic metaluminouscalc-alkalic (MCA) magma series, specialized subsets of metallogenycan be correlated with the oxidation state of the associated magmatism. Base metal (mainly Cu) expression empirically tracks oxidized calc-alkalic magmatism whereas Au-As metallogeny follows reduced calc-alkalic magmatism. Hence, the changes in metal specialization of porphyriticcalc-alkalic magma series as a function of both magma and crustal oxidation state is a major subtheme embedded within this text and accompanying roadlogs. At the end of this field trip, we hope to make a solid prima facie case that deposits in the Carlin Camp (Gold Strike in particular) are nothing more and nothing less than gold porphyries in the identical orthomagmatic sense that Yerington is a copper porphyry.
Key words
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