PLATINUM-GROUP METALS 



543 



ranes should be investigated as speculative resi- 

 dences of platinum metals. 



More specifically, integration of regional geologic 

 trends and the minor occurrences of platinum-group 

 metals throughout the gold placers of Alaska allows 

 one to speculate that large resources of platinum 

 metals exist in Alaska. If such resources exist, they 

 will be associated with three major ultramafic rock 

 belts, a major porphyry copper province, and the 

 alkalic rocks of the Seward Peninsula. 



The three major ultramafic belts — the Southeast- 

 ern Alaska, Kenai-Chugach, and Fairbanks-Livin- 

 good belts — are only partly explored, and new 

 ultramafic areas will undoubtedly be found in each 

 of these three belts. In addition, large areas of 

 Alaska, at present unmapped, may contain additional 

 ultramafic belts. Therefore, with the high potential 

 for undiscovered ultramafic host rocks and the wide 

 areal distribution of platinum metals in placer de- 

 posits associated with the ultramafic belts, the 

 potential for large platinum metal resources is very 

 high. 



The common occurrence of platinum metals with 

 porphyry copper deposits indicates that potentially 

 large resources of platinum metals may exist 

 throughout the 500-mile extent of the Alaska Range. 

 Locally within the Alaska Range, porphyry copper 

 deposits exist, and the potential for the discovery of 

 several new districts is very good. 



A belt of alkalic rocks approximately 200 miles 

 long exists in the eastern Seward Peninsula. To date 

 no analyses for platinum metals have been made, but 

 the potential of this area is very high, in light of 

 platinum metals associated with similar types of 

 rocks. 



PROSPECTING TECHNIQUES 



Prospecting for platinum metals has been, and 

 continues to be, rather intuitive. Perhaps the most 

 successful approach has been to look for placer ac- 

 cumulations of platinum metals by standard panning 

 techniques and then attempt to find the lode source. 

 After location of the lode source, normally a mafic or 

 ultramafic body, prospecting has been concentrated 

 on locating the oxide- and sulfide-rich zones with 

 which the platinum metals are commonly associated. 



Recent work by Clark and Greenwood (1972) on 

 the zoned ultramafics of southern and southeastern 

 Alaska has shown strong correlations of platinum 

 and palladium with specific major and trace elements 

 and rock types (table 114). Although the correla- 

 tions are consistent within an individual complex, 

 they differ between complexes. Similar correlations 



Table 114. — Correlations of maximum platinum-palladium, 

 concentrations, southeastern Alaska 



between rock and mineral types and trace elements 

 were noted by Page, Riley, and Haffty (1969; 1971). 



Analytical studies have also shown that the strati- 

 form and concentric ultramafic complexes are more 

 likely to contain platinum lodes than the alpine type. 

 Therefore, once a favorable type of ultramafic body 

 has been defined, the following procedure is most 

 effective: (1) sample and analyze all rock and min- 

 eral phases for platinum metals and associated trace 

 major elements such as Fe, Cr, Ni, V, Ti, and Cu; 

 (2) establish correlations between platinum metals 

 and rock elements ; and (3) define and sample areas 

 with highest correlation parameters as probable lode 

 sources. When utilizing this technique, it should be 

 remembered that the lode zone being sought is nor- 

 mally very thin, even though it may extend for a 

 long distance. Therefore any sampling done per- 

 pendicular to the layering must be close spaced. 



Recent studies by Cousins (1969, 1972) and Fuchs 

 (1972) show that both platinum and palladium may 

 be readily leached in the zone of weathering in source 

 rocks as well as in placers. This fact suggests that 

 regional geochemical prospecting techniques de- 

 signed to locate soluble and transported platinum and 

 palladium may be an effective way to locate poten- 

 tial platinum metal lode sources. Soil sampling for 

 platinum metal lodes may also be effective if one 

 looks for the more stable platinum metals such as 

 Os, Rh, Ir, and Ru. An attempt was made by Rudolph 

 and Moore (1972) to define lode sources using geo- 

 botanical prospecting; they reported that species of 

 Eritrichiiim chamissonis, DC. contained up to 4.8 

 ppm platinum collected from the Red Mountain ultra- 

 mafic mass at Goodnews Bay, Alaska. Other at- 

 tempts to use this method have been unsuccessful (J. 

 B. Mertie, written commun., 1972) . 



Platinum metals do, however, occur in many di- 

 verse geologic settings, particularly with copper 

 deposits, and the techniques of exploration for these 



