Isotope and fluid inclusion studies of geological and hydrothermal processes, northern Peru
- Florida International Univ., Miami, FL (United States)
- Cd. Universitaria, Coyoacan (Mexico)
- Lawrence Berkeley Lab., CA (United States)
Mineralization in the Hualgayoc district of northern Peru occurs in altered Miocene felsic intrusions and in mid-Cretaceous platform sedimentary rocks of the Goyllarisquizga, Inca, and Chulec formations. The ores occur both as stratiform and stratabound pyritiferous base-metal deposits (mantos), and as steeply dipping, sedimentary and intrusive rock-hosted base-metal veins. Igneous rocks in the district are affected by propylytic, sericitic-argillic, sericitic, potassic, and acid-sulfate alteration. K-Ar and Rb-Sr dating and geological evidence indicate multiple stages of intrusive activity and hydrothermal alteration, including close spatial emplacement of two or more separate Miocene magmatic-hydrothermal systems. K-Ar dates on sericite, hydrothermal biotite, and alunite indicate that the most important hydrothermal episodes in the district took place {approx}13.24 and 12.4 Ma. Other K-Ar dates on altered rocks in the district may reflect various amounts of resetting by the emplacement of the 9.05 {+-} 0.2 Ma Hualgayoc rhyodacite. A five-point Rb-Sr isochron for the San Miguel intrusion at Cerro Coymolache yields an age of 45 {+-} 3.4 Ma, which indicates much earlier magmatic activity in this area than recognized previously. Fluid inclusion and paragenetic studies reveal a clear temporal evolution of fluid temperature and chemistry in the San Agustin area at Hualgayoc. Gradually, ore formation shifted to precipitation of vein minerals in the brittle fractures as the mantos became less permeable and were sealed off. Vein formation continued from progressively cooler and more diluted fluids (down to {approx}150{degrees}C and 4.3 wt% NaCl equivalent) as the system waned. No evidence for phase separation is observed in the fluids until the very last paragenetic stage, which contributed no economic mineralization. 53 refs., 15 figs., 7 tabs.
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 456727
- Journal Information:
- International Geology Review, Vol. 36, Issue 7; Other Information: PBD: Jul 1994
- Country of Publication:
- United States
- Language:
- English
Similar Records
[sup 40]Ar/[sup 39]Ar isotopic dates from the Cripple Creek gold-Telluride district, Colorado: Constraints on the timing of magmatism and mineralization
Temporal relations of volcanism and hydrothermal systems in two areas of the Jemez volcanic field, New Mexico