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

Abstract

We appreciate the comments of G.D. Langstaff and the opportunity to elaborate on the origin of Carlin-type gold deposits. Langstaff focuses on two of the critical issues regarding these deposits, their age and spatial association with igneous rocks. Although his comment mentions almost every known Carlin-type deposit, our reply focuses on deposits in major districts. Direct dating of hydrothermal minerals and indirect dating based on crosscutting relations with pre-, syn-, or postmineral rocks in Nevada have demonstrated that major deposits in all trends are Eocene (Emsbo et al., 1996; Leonardson and Rahn, 1996; Phinisey et al., 1996; Groff et al., 1997; Hall et al., 1997, 2000; Hofstra et al., 1999; Hofstra and Cline, 2000; Johnston, 2000; Ressel et al., 2000a, b; Tretbar et al., 2000). Although many Carlin-type deposits are not dated, we emphasize that no deposit has been demonstrated to be any other age. Preliminary 40Ar/39Ar dating of white micas from mineralized Eocene dikes at Meikle and Griffin in the Carlin trend gives Eocene ages (Ressel et al., 2000b). Any discussion of the origin, especially spatial association, of Carlin-type deposits with igneous rocks must emphasize the northern and central Carlin trend (Fig. 1). Deposits there constitute ~60 percent of the total estimated contained gold in Carlin-type deposits of Nevada and Utah (Hofstra and Cline, 2000). We interpreted the 700 km2 aeromagnetic anomaly (Fig. 1) there to reflect an underlying composite Eocene intrusion emplaced between about 40 …