A pilot study was carried out on two relatively deep drill-cores (??? 600 m) from the Go??temar Granite massif in S.E. Sweden. This granite is typical of the 1400-Ma anorogenic granites of the northern hemisphere. Samples from representative, unfractured parts of the cores, together with four samples taken along a profile tangential to a fracture plane at ??? 280-m depth, were investigated chemically, mineralogically and isotopically. The results show that after crystallisation, subtle and pervasive open-system modifications of the trace-element chemistry of the granite took place. Whereas the major-element chemistry and minera-logical data emphasised the relative homogeneity of the Go??temar Granite samples investigated, trace elements such as U, Rb, and Pb revealed irregular distributions which are probably the result of large-scale hydrothermal alteration processes. This conclusion is supported by isotopic studies which indicate that whole-rock samples were open to a gain or loss of Pb and possibly U at ??? 420 ?? 171 Ma ago. In addition, isotopic data for U-Pb and U-Ra are consistent with a recent minor loss of U. The pervasive alteration and the more recent mobilisation of U are evident to a depth of at least 600 m. The effects are most prevalent along major fracture zones and within the upper 250-300 m of one drill-hole where a high frequency of crush zones has been noted. Higher Fe oxidation ratios, higher Rb contents, lower U contents and correspondingly higher Th/U ratios, all characterise this zone. ?? 1985.
Additional Publication Details
Element mobility studies of two drill-cores from the Go??temar Granite (Kra??kema??la test site), southeast Sweden