Post-early Cretaceous MVT zinc-lead mineralisation, Bongara area, northern Peru: Fluid characteristics and constraints on deposition mechanisms.
Published: 2006
Language: eng
Number of pages: 317
ISBN-13: 9780494218679
Description: Thermochemical sulphate reduction (TSR) was probably the principal H 2S production mechanism for metal precipitation as indicated by: (1) delta 34S values of sulphides from -13.7 to +19.3&permil; V-CDT; (2) the presence of evaporite-bearing horizons in the Triassic and Jurassic formations of the Pucara Gp., and (3) fluid inclusion homogenization temperature data. The sources of sulphate were probably Late Cretaceous seawater and also evaporite-bearing rocks of the Mid-Late Triassic and Late Jurassic. A comparison with twelve other MVT deposits/districts suggests that: (1) the most important metal precipitation mechanism in MVT systems appears to be TSR; (2) mixing between organic matter-derived H2S and ore fluids may be the next most important mechanism; and (3) carbonate associated with TSR usually has delta13C values typical of inorganic marine carbonate. The delta13C values of dolomite in the Bongara area (-3.2 to +1.9&permil; PDB) indicate a predominant inorganic carbon source.Mineralization in the Bongara area, hosted by late Triassic-Jurassic carbonate rocks, shows definite similarities to Mississippi Valley type (MVT) systems worldwide. In the paragenetic sequence there are two dolomite types: early, pre-ore dolomite (D1), and late dolomite (D2). Fluid inclusions in dolomite and sphalerite are characteristic of MVT systems (&sim;78--187  0C; &sim;15--23 wt% CaCl2 equivalent). The cathodoluminescence (CL) characteristics of carbonates correlate over &sim;60 km, indicating a regional scale, interconnected hydrothermal system. CL observations indicate that D1 dolomite has no zonation, whereas D2 dolomite is characterized by four growth zones: D2-a, -b, -c and -d. The D2-b zone is closely associated with sphalerite and galena.Fluid inclusions in dolomite show a temperature decrease from north to south. Electron microprobe analysis shows a trend of lower Fe, Mn and Ca and higher Mg contents in D2-dolomite in the southern location, which also has some more enriched delta18O values than the northern and central locations. These variations suggest that a general southward regional hydrothermal fluid flow was responsible for mineralization in the Bongara area; the depth is estimated at &sim;2000--3000 m. Fluid flow is interpreted to have been related to the Peruvian orogenic event (Late Cretaceous) in northern Peru/Ecuador.
Notes: Source: Dissertation Abstracts International, Volume: 68-01, Section: B, page: 0156.

Thesis (Ph.D.)--University of Toronto, 2006.

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