The Heavy Accessory Minerals of the Val Verde Tonalite

Citation

Wilson, Robert Warren (1936) The Heavy Accessory Minerals of the Val Verde Tonalite. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/6h66-9w75. https://resolver.caltech.edu/CaltechTHESIS:10162023-153512856

Abstract

The construction of the Metropolitan Water District Aqueduct for Los Angeles County, California has necessi­tated the drilling of long tunnels at various points en route from the Colorado River. One such tunnel situated near the town of Val Verde, California passes through some seven miles of tonalite. About a dozen samples of the tonalite were taken at approximately half-mile inter­vals in the Val Verde tunnel. These samples were studied to determine the accessory constituents present, and their variation in the section exposed in the tunnel.

The non-magnetic or weakly magnetic heavy accessory minerals consist of sphene, apatite, epidote-clinozoisite, zircon, zoisite, allanite?, pyrite, and calcite? in approx­imately decreasing order of abundance. From samples at one end of the tunnel tourmaline, monazite, abnormal blue anatase, and thulite? were recorded. Associated with the appearance of tourmaline and the other minerals just cited is an increase in zircon and decrease in apatite, suggest­ing a more acid phase in the tonalite at this point. An explanation may be furnished by the fact that the tonalite is here closer to overlying and intruded schists, and hence to the margin of the former.

The more magnetic minerals of the tonalite were bio­tite and hornblende (15%-30% of entire rook), and accessory magnetite.

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