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T-4518 52 <br />Quartz (up to 2 cm in length) and pyrite (up to 1 cm) fill fractures crosscutting; <br />fine-grained quartz-pyrite in the second stage of mineralization (Fig. 316). The two <br />quartz-pyrite stages commonly occur in poorly- to well-banded veins (Figs. 29f and 31a). <br />The fine-grained quartz tends to comprise the margins while the coarser quartz fills ttie <br />central portion of veins. Euhedral pyrite grains are surrounded by quartz crystals, <br />suggesting that quartz deposition continued after pyrite deposition (Fig. 32a). Serici~:e <br />locally deposited on euhedral quartz. <br />Pyrite is often replaced by base- and precious-metal sulfides. Replacement <br />minerals are present along fractures but irregulaz blebs of later sulfide minerals in pyrite <br />(Fig. 32b) are equally common. More than 50% of the original pyrite is commonly <br />replaced (Fig. 32c). <br />Speculaz hematite, sphalerite, and galena are locally present in the later quartz- <br />pyrite stage. Specular hematite (10-200 µm) coats euhedrat quartz as open space fillings <br />and is surrounded by later euhedral quartz, thus it occupies a hiatus in quartz deposi~ion. <br />Euhedral blades of hernadte and contemporaneous sphalerite are surrounded by sub}iedral <br />to euhedral quartz (Fig. 33a). Euhedral quartz crystals surround irregular galena an~i <br />sphalerite grains (Fig. 33b). <br />Anhedral to euhedral, fine-grained (less than 1 mm), dolomite, calcite, and possibly <br />ankerite occur as open space filling after the medium- to coazse-grained quartz-pyrite <br />stage (Fig. 34a). A lack of twinning prevented precise idenrificadon of the carbonate <br /> <br />