| Description |
xv, 170 leaves : illustrations, photographs (some colored) ; 29 cm |
| Summary |
"The Acari Iron Mining District, part of a tilted uplifted fault block, comprises an area about 300 square kilometers, in the southern part of the coastal belt of Peru. It is in the foothills of the western range of the Andes and it is dominantly formed by granodioritic and granitic intrusive rocks which belong to the Andean batholith of Cretaceous-Tertiary age. The intrusive rocks are overlain by a central, elongated, northwest trending band, of metasedimentary and volcanic rocks. The magnetite deposits of Acari district are long, dike-shaped bodies, which fill two systems of fractures in the granodiorite intrusive, located in the southwest portion of the district. One fracture system, includes both the Mastuerzo and Campana Zone, has NWN trend. The other fracture system, the Pongo Zone, trends NE. The ore consists predominantly of black, massive, compact, microporous, fine-grained magnetite characterized by colloform texture. Its average grade is about 60-66% Fe with 0.10-0.20% P. The deposits are characterized by a vertical zoning which plunges southward, consisting of: 1) an upper magnetite ore zone, 2) a transitional zone, and 3) a lower barren amphibole zone. Two successive stages of fracturing and faulting, one forming transverse faults, the other longitudinal faults, have affected the magnetite deposits. The deposits are believed to have resulted from two principal endogenetic processes, one was the injection of rich-iron fluids into fractures in the granodiorite intrusive, the second was hypogenetic alteration of the magnetite deposits by barren hydrothermal solutions, which probably were derived from the crystallization of the granite intrusive in the northeastern portion of the district. Three stratiform hematite deposits containing, about 31-37% Fe occur within the outcrop area of Mississippian (?) age of metasedimentary rocks at the headwater of the Loza Valley. Fairly consolidated black magnetite sands overlie the granite intrusive in Cerro Conchudo. They contain approximately 6% Fe. Copper veins consisting of discontinuous ore shoots of oxidized minerals in long, east-west trending fissures occur within the granite intrusive, or as fractures filling in felsic dikes or quartz veins within the Dark Volcanics and within the granodiorite intrusive "--Abstract, leaves xiv, xv. |
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