DIKE-HOSTED ORES OF THE BEAST DEPOSIT AND THE IMPORTANCE OF EOCENE MAGMATISM IN GOLD MINERALIZATION OF THE CARLIN TREND, NEVADA-A DISCUSSION

摘要

Sir: Ressel et al.'s (2000b, p. 1417) assertion that "Eocene magmatism is considered the major process that drove hydrothermal circulation, which formed Carlin-type deposits of the Carlin trend" and conclusion (p. 1438) that 'Deposits of the northern Carlin trend should be considered pluton related" are not supported by credible evidence.Ressel et al. (2000b) attributed the 700 km~2 aeromagnetic anomaly south of the Carlin trend to an Eocene pluton, based on the association of exposed Eocene stocks with aeromagnetic anomalies and on the presence of Eocene dikes within and beyond the anomaly. The same reasoning could equally well support attribution of the anomaly to Jurassic or Cretaceous plutons. The Jurassic Contact pluton (Coats, 1987) and the Cretaceous Osgood pluton (Berger; 1985) have aeromagnetic anomalies (Hildenbrand and Kucks, 1988). On the Carlin trend, a Jurassic stock occurs at Post-Betze and related dikes extend farther north (Ressel et al., 2000a). A Cretaceous intrusion crops out in the northern part of the 700 km~2 anomaly and Cretaceous dikes occur in the Carlin mine (summarized by Hofstra et al., 1999). An anomaly associated with the Cretaceous, copper-rich Mike deposit has been attributed to an underlying pluton (Teal and Branham, 1997). Thus, there is no evidence that the 700 km~2 anomaly is due to an Eocene pluton rather than to a Jurassic or Cretaceous one.