Abstract

Iron deposits of California that cluster around small intrusive bodies and are localized in metamorphosed limestone or dolomite show varying degrees of mineralogic complexity. Minerals present along with those that more commonly occur in contact metasomatic deposits in the United States include chondrodite, humite, clinohumite, ludwigite, ilvaite, idocrase, spinel, and forsterite. One deposit is characterized by the very simple mineral assemblage calcite, antigorite, and magnetite except within a few feet of an intrusive body. Generally, pyroxene, garnet, chondrodite, humite, and clinohumite formed early; antigorite, magnetite, specularite, and goethite formed late. The writer suggests several sequences of mineral deposition and compares them with sequences determined by others.

Addition of material and replacement were prominent in the formation of these deposits. Iron was added during the formation of magnetite, hematite, and goethite and probably also during the formation of hedenbergite, andradite, ludwigite, ilvaite, and epidote; fluorine during the formation of chondrodite, humite, and clinohumite; boron during the formation of ludwigite; and probably magnesium during the formation of chondrodite, humite, clinohumite, and antigorite. Some recrystallized limestone was replaced by magnetite and antigorite; some antigorite was replaced by magnetite; some pyroxene, minerals of the humite group, and spinel were replaced by magnetite.

The writer classes the deposits as contact meta-somatic but suggests that the mineralogy indicates a temperature range from high contact metamophic to moderate hydrothermal activity.

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