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places, these rocks contain vesicles and ocelli lined with carbonate minerals, indicating that COZ <br />• concentrations were high in the melts. <br />Figure 3: Samples of <br />nepheline monzosyenite <br />from South Cresson. Dark <br />minerals are biotite, augite <br />and magnetite. Light <br />minerals are orthoclase, <br />1.~ <br />District scale alteration mapping has shown that many of these intrusions generated their own <br />hydrothermal systems, as they are commonly shrouded by halos ofbiotite-magnetite-orthoclase <br />± pyrite alteration (discussed below). These rocks are also strongly carbonated, with cazbonates <br />replacing mafic igneous minerals. It is not clear if the cazbonation was related to a process of <br />autometasomtism or has been superimposed upon the rocks of group B by later episodes of <br />hydrothermal alteration. <br />2.5 Late Stage MaTic/Ultramafic Intrusions <br />Following [he emplacement of the breccias, phonoli[es, and intermediate rocks, a series of mafic <br />to ultramafic dikes, sill-like bodies and small breccia pipes were emplaced. While <br />volumetrically subordinate to other rock types (< 2% of all rocks), they comprise an important <br />group as they are associated with a disproportionate share of gold mineralization. In the past, <br />these rocks have been considered as a single group (see Lindgren and Ransome, 1906, p. 90-97). <br />However, they span a considerable range of compositions (groups C and D, figure 1), ranging <br />from ultramafic rocks with <30 wt % SiOZ, to rocks which have the characteristics of alkaline <br />basalts (trachybasalt field, figure 1). They can broadly be divided into two groups; those with <br />mafic characteristics (alkali-rich basalts with high volatile concentrations; group C) and those <br />with ultramafic chazacteristics (<40wt% SiOZ; group D). These types form distinct groups based <br />on whole rock geochemical analyses, but somewhat of a continuum may exist between the two. <br />Unfortunately, these rocks are almost always pervasively altered to clay and carbonate minerals <br />• (referred to as decomposition by Lindgren and Ransome, 1906), which precludes the use of <br />Cripple Crcek B ~•irmr G°N m/ning Co. Shepherd Millcr./nc. <br />iID/AI/ONDIP~D.WEII°O]6TRynrtuvadina~!.Jor 6 MnrCh 1000 <br />