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T-4518 82 <br />microprobe study. They include: famatinite, tennantite, proustite, pyrazgyrite, and <br />stromeyerite (reported by Hennigh (unpub. data} in the district) in the sulfosalt stage and <br />digenite and blaubleibender covellite in the supergene stage. <br />The study of alteration in the Cross deposit resulted in a comprehensive alu;ration <br />scheme which relates major vein stages to specific alteration assemblages. A muscovite- <br />sericite-phengite-chlorite (MSPC) alteration assemblage developed during quartz-I~yrite <br />mineralization. Macroscopically visible adularia alteration developed during speculaz <br />hematite mineralization. Cazbonate (dolomite and calcite) alteration developed dining <br />cazbonate mineralization. Adularia and ankerite were added to the MSPC alteration <br />assemblage during base- and precious-metal mineralization, A smectite-kaolinite <br />alteration assemblage developed during late dolomite mineralization. <br />SLmmarV of the Sea~ence of Events <br />Structural, mineralogic and alteration events which formed the Cross deposit <br />occurred in the following sequence. <br />East-trending compression activated left-lateral movement on the Arapahoe Pass <br />(AP)-Junction Ranch (JR) fault. <br />2. Dilation zones developed at a jog in the AP-JR fault and localized the Caribou <br />stock and quartz monzonite dikes. <br />3. The direction of compression rotated to the northeast at either a Iocal or a regional <br />scale. If rotation occurred at the local scale, left-lateral movement on the .AP-JR <br />fault conrinued, If rotation occurred at the regional scale, left-lateral movement on <br />the AP-JR fault ceased. <br />