Stable isotope and fluid inclusion studies of carbonate deposits from the Tolfa Mountains mining district (Latium, central Italy)
✍ Scribed by U. Masi; V. Ferrini; J. R. O'Neil; J. N. Batchelder
- Publisher
- Springer
- Year
- 1980
- Tongue
- English
- Weight
- 610 KB
- Volume
- 15
- Category
- Article
- ISSN
- 0026-4598
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✦ Synopsis
Carbon and oxygen isotooe analyses were made of representative samples of calcite and quartz from the carbonate deposits in the Tolfa Mountains mining district. Measurements were also made of hydrogen isoto~)e compositions, filling temperatures and salinities of fluid inclusions in these minerals.
There are three stages of mineralizalion at Tolfa. In stage I, characterized by calc-silicate hornfels, the carbonates have relatively high 5 180 values of 14.5 to 21.6 suggesting a rather low water/rock ratio. 513C values of -0.3 to 2.1 indicate that appreciable decarbonation or introduction of deep-seated carbon did not occur. Stage Ills marked by phanerocrystalline carbonates; 6 180 values of 13. 1 to 20.0 and 613C values of 0.7 to 5.0 identify them as hydrothermal veins rather than marbles. 6 D values of -56 to -50 for inclusion fluids suggest a possible magmatic component to the hydrothermal fluid. Filling temperatures of coarse-grained samples of Calcite II are • 309o to 362 ° C with a salinity range of 5.3 to 7. 1 weight percent NaCI. Calculated 5 180 values of 11-12 for these fluids are again indicative of low water/rock ratios. The sparry calcites of stage III have 518Oand 513C values of 8. 1 to 12.9 and -I. 7 to 3.2, respectively. 5 D values of inclusion fluids are -40 to -33, clearly heavier than in earlier stages and similar to values of modern local ground waters. A salinity measurement of <0. 1 weight percent NaCI in a sample of Calcite III is compatible with a relatively unaltered ground water origin for this fluid. Precipitation of the sparry calcite took place at much lower temperatures, around 160 ° C. For quartz, 6180 values of 9.3 to 12.4 and 5D values for inclusions of -53 to -28 are consistent with its late occurrence and paragenetic link with associated carbonates.