Mina de Sn San Rafael Peru.pdf

8/10/2019 Mina de Sn San Rafael Peru.pdf

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Constraints on the genesis of lode-style tin mineralization: evidence from

the San Rafael tin-copper deposit, Peru

Michael S.J. MlynarczykMay 2005


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Plan of the presentation

Tin metallogeny in the Central Andes

The San Rafael Sn-Cu deposit:- structural geology- alteration

- mineralization- fluid inclusions- stable isotopes

Genetic model


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The metallogeny of the Central Andes


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A collisional model for tin metallogeny


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The San Rafael tin deposit

~ 1,000,000 tonnes Sn metal, average grade ~ 5 wt.% Sn


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Geology of the San Rafael area

granite

slate


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One major vein-breccia system (the San Rafael lode)


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Variation in normative mineralogy: early sericitic andtourmaline alteration versus main-stage chloritization

Freshgranite


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Chemical zoning of hydrothermal tourmaline:from early dravite (Mg) to ore-stage schorl (Fe)


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Physico-chemical conditions of chloritic alteration

associated with main-stage cassiterite deposition


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Ore mineralogy and metal zoning

cas

Upper zone: sulfides dominate, complex mineralogy(chalcopyrite, pyrite, arsenopyrite, sphalerite, galenapyrrhotite, needle-tin cassiterite, quartz, chlorite)

Lower zone: oxides/silicates dominate, simple mineralogy(massive cassiterite, quartz, chlorite wolframite)


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Fluid inclusion studies

18 m

15 m

qtz

cas

Ore fluids of moderate T(360-230C) and fluctuatingsalinity (21-0 wt.% NaCl eq.)


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Stable isotope studies

34 S V-CDT ()

18 O V-SMOW ()

18 O V-SMOW ()

cas

qtz

chl wol


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Isotopic evolution of hydrothermal fluids at San Rafael

Calculated valuesof 18 O and D forwater in equilibriumwith the different oreand gangue minerals(at the temperatureof their formation),exhibit a clearparagenetic trendof 18 O decrease.


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Mineral stabili ty relationships for the tin stage (II) and thecopper stage (III) of the San Rafael paragenesis


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Effect of cooling and mixing of magmatic and meteoricfluids on the oxygen isotope composition of

precipitating quartz (A) and cassiterite (B)

Only a scenario of mixing of a hot brine with a cooler,dilute fluid can reproduce the range of oxygen isotope

compositions of quartz and cassiterite from the deposit


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A genetic model for San Rafael

qtz

cas

Early stage: lithostatic conditions, hot magmatic brines produce strongsericite + tourmaline alteration and sealed, barren, tourmaline-quartz veins.

Main ore stage: mixing of magmatic brines and meteoric waters in the fault- jogs oxidation, dilution, cooling, and acid neutralization of the ore fluids massive precipitation of cassiterite as localized, high-grade ore shoots.

Tectonic activity reopens the vein system transition to hydrostatic

conditions + influx of heated meteoric waters.


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Thank you for your attention...

Mina de Sn San Rafael Peru.pdf

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