- 作者: 王源; 楊昭男
- 作者服務機構: Department of Geology National Taiwan University
- 中文摘要: Volcanic geology of the Chimei copper prospect area, eastern Taiwan has beeninvestigated in considerable detail, and the results are discussed in relation toregional geology and the genesis of the pyrite-chalcopyrite deposits. The so-called "Chimei andesites" can be divided, based on ample field criteriaand petrography, into the Tienkangshan diabase, the Tewu pyroxerie andesite, theChimei pyroxene-hornblende andesite, and the Wantan hornblende andesite, in theascending order. They are overlain by the Tuluanshan Formation (lower Miocene)subsequently. These older rocks are disconformably covered by the Plioceneflysch sequence of the Paliwan Formation. The Penglai orogeny brought theminto folding and faulting at early Pleistocene. After the orogeny, the Liyachinshanhornblende andesite, which formed several well-preserved new volcanoes, and prac-tically escaped from the pervasive hydrothermal alteration, came resting -on theothers unconformably. The Tienkangshan diabase with dike swarms of a fine-grained pyroxene andesiteseems to be the oldest rock encountered in this area as exposed and also penetratedby many boreholes. This rock unit seems to attain thickness of about 100-150 m,and in some boreholes intercalated with other older andesites. The mutual relationof these units is still unknown. They are usually strikingly altered and/or zeolitized.These rocks may represent one of the oldest rock formations exposed in the CoastalRange. As far as the surface observation and subsurface exploration are concerned, thepyrite-chakopyrite deposits here are found sporadically in the two agglomeratichorizons of the Chimei pyroxene-hornblende andesite, and thus a strata-bound originhas been considered. Further enrichment in the form of small veinlets, however;is also evident, although the secondary mobilization of copper seems to have takenthe form of sporadic patches without extending beyond the above stratigraphichorizons. Field coincidence of the diabase and rich copper bonanzas has been noticed, butits significance is not yet clear. Further study along this line is deemed meaning-ful. Small-scale but efficient exploration and exploitation of the separate bonanzasshould further be encouraged in this type of ore deposits.
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