Hydrothermal Rhyolitic Alteration in the Castle Mountains, California

Abstract

INABSTRACT X-ray diffraction, differential thermal, chemical analysis and cation exchange data indicate a progressive genesis upon hydrothermal alteration of rhyolitic materials in an extensive fault zone. Kaolinite, a Ca-Mg beidellite, mixed-layer beidellite-hydrous mica and beidellite-vermieulite clay minerals, quartz, cristobalite and feldsp~ r commonly occur in the deposit.Detailed studies show that the sequence of the 2 ." 1 clay mineral alteration is beidellitehydrous mica mixed-layer -+ beidellite-vermiculito mixed-layer --> beideUite. This mineralogical change parallels a progressive decrease in the layer charge and amount of fixed K + present and an increase in exchangeable Ca + and Mg + respectively.

Fe3+-Rich Montmorillonite-Beidellite Series in Ayvacik Bentonite Deposit, Biga Peninsula, Northwest Turkey

“…In beideLlite, (Si7AsAlo.ss)(A14.o0)O2o(OH)4Xo.85nH20, the charge arises from AP* in tetrahedral sites; X is a monovalent interlayer cation. The structural formula of the montmorillonite-beidellite series as given by Heystek (1963) is: (a) (Siv.27A10.v3)(A13.66Tio.0 3Fe3+0.o~ -Mg0.39)Cao.31Nao.02Ko.osO20(OH)4, based on samples from the Castle Mountains, California, (13) (Si6.ovAlz.o3)(A1398-Fe 3 +o.oaMgo.oz)Nao.91Ko.ozO2o(OH) 4, Black Jack Mine, Idaho (Weir, 1965), (c) (Si749AIo.51)(AI3.49Fe 3 +o.o2Mgo~53)-Nao.9oKo.0102o(OH)4, Unterrupsroth, Germany (Weir, 1965). The structural formulae based on the Ayvacak samples are: (9) (Si7.52Alo.4s)(A13.otFe 3 +o.o2Mgo.ov)fao.oo7-Nao,01Ko,o4Ozo(OH)4 , (7) (Siz,,Alo.56)(A127oFe 3 +o.64Mgo.s0)-Cao.07Nao.15Ko.t202o(OH)4 , (5) (Si7.48A10.sz)(AlzTzFe 3 +o.6o-Mgo.78)Cao.o9Nao.14Ko.160~o(OH)4.…”

“…The above structural formulae of Ayvaclk low-charge beidellites indicate the presence of chlorite or a chloritic interlayer. According to Weir (1965) and Heystek (1963), the total interlayer charge of ideal beidellites is >0.85 per unit cell, and >50% of the layer charge is from tetrahedral substitutions. The Ayvaclk montmoriltonite-beidellite series has a layer charge of <0.52 per half unit cell and <50% of the interlayer charge arising from tetrahedral substitution, except sample 9 (Table 4).…”

Studies on a red-colored soil derived from basaltic andesite of siiibayama

“…(5) and KINOSHITA and TANAKA (7) have also discussed the decrease of Si content of rocks during alteration and of the iron mineral species of the iron ore, respectively. The alteration sequence of clay mineralogical composition from the acidic alteration center to the alkaline margin or intratelluric zone has been generally observed (lw AO (14), STEINER (15), HEYSTEK (16), and SCHWARTZ (17)_ According to KINOSHITA and MUTA (18), pH value of hydrothermal solution gradually rises from the center to the margin of alteration zone, because the solution permeating through rocks dissolves basic compounds. The pH value of the solution is high at the deep intratelluric part as the acidity due to sulfuric acid formation decreases because of the lack of 0 2 _ At the margin of the alteration zone or the intratelluric place, smectite can be produced by hydrothermal alteration.…”