Metal Sources in Stratabound Ore Deposits in the Andes (Andean Cycle) — Lead Isotopic Constraints

Fontboté, Lluı́s; Gunnesch, Klaus A.; Baumann, A.

doi:10.1007/978-3-642-88282-1_60

Cited by 10 publications

(2 citation statements)

References 36 publications

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“…However, Orr (1974) (Fig. 23), should be expected (Fontbot• et al, 1990b). Gunnesch et al (1990) have also measured the lead isotope composition of host-rock carbonates in the San Vicente sequence without directly associated orebodies.…”

Section: Sulfur Isotopesmentioning

confidence: 99%

Genesis of the mississippi valley-type Zn-Pb deposit of San Vicente, central Peru; geologic and isotopic (Sr, O, C, S, Pb) evidence

Fontboté¹,

Gorzawski²

1990

Economic Geology

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The San Vicente Zn-Pb ore deposit is situated 300 km east of Lima in central Peru, within the Upper Triassic-Lower Jurassic carbonate platform (Pucarft Group) at the western margin of the Brazilian Shield. Production during the last 20 years and present reserves exceed 12 million tons of ore assaying about 12 percent Zn and 1 percent Pb. Sphalerite and galena, the only ore minerals, occur as lens-shaped bodies generally parallel to the bedding. Within the 1,400-m-thick Pucarfi sequence three ore-bearing dolomite units occur. The ore lenses are bound to dolomitized tidal fiat and lagoon facies with cryptalgal lamination and evaporite molds and to adjacent oolithic grainstones of barrier facies. Strontium, carbon, oxygen, and sulfur isotope geochemistry was carried out on consecutive crystallization generations. The results obtained display systematic trends. The 87Sr/S6Sr ratios range between 0.7077 and 0.7084. The first generations display values very similar to those of Upper Triassic-Lower Jurassic ocean water. Later generations are slightly enriched in radiogenic strontium. The degree of enrichment in radiogenic strontium is low compared to other Mississippi Valley-type deposits. The b180 values range between-6 and-10 per mil PDB, and the b•3C values between +2 and-1 per mil PDB. The late crystallization generations are enriched in the light isotopes of oxygen and carbon compared to the first generations. The sulfur isotope ratios of sphalerite are relatively homogeneous, ranging between 9.9 and 13.0 per mil. A trend to lighter sulfur isotope ratios with advancing diagenetic stage can also be recognized. The San Vicente lead-zinc deposit formed during burial diagenesis. The temperatures indicated by sulfur isotope geothermometry (75ø-92øC) would be consistent with temperatures reached at a burial depth of about 2 to 3 kin. This might have been reached by the end of the Jurassic. A model based on abiogenic reduction of sulfates at or near the ore site, and the introduction of a zinc-and lead-bearing basinal brine characterized by strontium isotope ratios slightly higher than contemporaneous seawater and highly radiogenic lead, is favored. The association of the orebodies with peritidal facies with abundant sulfate molds is important evidence favoring the existence of two separate reservoirs for sulfur and metals. Leaching of detrital material derived from Precambrian upper crust from the Brazilian Shield would explain both strontium and lead isotope ratios.

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Section: Sulfur Isotopesmentioning

confidence: 99%

Genesis of the mississippi valley-type Zn-Pb deposit of San Vicente, central Peru; geologic and isotopic (Sr, O, C, S, Pb) evidence

Fontboté¹,

Gorzawski²

1990

Economic Geology

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“…the mine Mantos Blancos). Their origin was linked to the geotectonic setting of the Jurassic to Lower Cretaceous arc (Fontbote et al, 1990a). Such deposits were ascribed to a mantle source by lead isotope constraints (Fontbote et al,199Ob).…”

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confidence: 99%

Generation and metamorphism of new crust in magmatic arcs: a case study from northern Chile

Lucassen

Franz

1992

Terra Nova

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In a deep section of the Jurassic Andean arc, coastal Cordillera of northern Chile, south of Antofagasta, basic magmas from a mantle source accreted large masses of crust in an early stage of arc development. These gabbroic intrusions were isochemically metamorphosed at moderate pressures (≤ 5 kbar) and high temperatures (∼ 800°C) into uniform garnet‐absent dino+ortho‐pyroxene gneisses (granulites). Subsequently they were partly transformed into amphibolites (T≤ 700°C) during tectonically controlled access of fluid without major changes in whole rock chemistry. Locally migmatization occurs in the amphibolites. The metamorphic unit was diversified by enduring magmatic activity in the form of chemically distinct gabbroic and quartz dioritic intrusions. Formation and composition of continental crust might be a typical example for the deeper plutonic sections of this continental magmatic arc.

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Das „Zentrallaboratorium für Geochronologie“ (ZLG) in Münster – Zwei Jahrzehnte geowissenschaftlicher Forschung an einer „DFG‐Hilfseinrichtung“

Grauert¹,

Baumann²

2000

Fortschritte Geowissenschaftlicher Forschung

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Metal Sources in Stratabound Ore Deposits in the Andes (Andean Cycle) — Lead Isotopic Constraints

Cited by 10 publications

References 36 publications

Genesis of the mississippi valley-type Zn-Pb deposit of San Vicente, central Peru; geologic and isotopic (Sr, O, C, S, Pb) evidence

Genesis of the mississippi valley-type Zn-Pb deposit of San Vicente, central Peru; geologic and isotopic (Sr, O, C, S, Pb) evidence

Generation and metamorphism of new crust in magmatic arcs: a case study from northern Chile

Das „Zentrallaboratorium für Geochronologie“ (ZLG) in Münster – Zwei Jahrzehnte geowissenschaftlicher Forschung an einer „DFG‐Hilfseinrichtung“

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