Laserfiche WebLink
T-4518 77 <br />Cazbonate alteration developed during carbonate mineralization. It occurs <br />primarily with MSPCAA alteration as rhombohedral carbonates replacing quartz and, less <br />commonly, other minerals from grain boundaries. A lack of twinning prevented precise <br />identification of the cazbonate minerals. Macroscopically, the alteration is identical o~ <br />MSPCAA alteration (Fig. 46c). <br />Muscovite-Seri cite-Phenpi te-Chlorite-A dula rice-A nkeri to <br />The disequilibrium assemblage of muscovite-sericite-phengite-chlorite-adulari.a- <br />ankerite (MSPCAA) alteration developed during base- and precious-metal deposition. <br />The textures and distribution of muscovite, sericite, phengite, and chlorite are similaz to <br />those found in MSPC alteration, which it overprints. Medium-grained chlorite and <br />phengite are less common, however. MSPCAA alteration may simply represent an <br />addition of adularia and ankerite to MSPC alteration. <br />Adularia was identified as previously described. l.ow Mg ankerite <br />(Ca(Mg,Fez+,Mn)(C03)~ was tentatively identified by SEM analyses: it contains the <br />elements Ca and Fe with minor Mn. Ankerite of unspecified composition was report~;d by <br />Dentler (1984). The identification here is questionable because no natural occurrence; of ~ • <br />ferrodolomite [CaFe(COg)2] is recorded and experimental work suggests that ankeriie - <br />may contain a maximum of only 75% of the Fe endmember (Fe,MnC03)•CaC03 (Deer et <br />al., 1966). <br />A cross-section through MSPCAA alteration in monzonite displays three zones. <br />The innermost zone adjacent to the vein consists of: 1) fresh igneous orthoclase and <br />