We appreciate the comments on our paper on the Post-Betze sediment-hosted disseminated gold deposit which indicate that clarification is required. Ilchik suggests alternative interpretations of our findings with regard to two main issues: the nature of the sill that we have described as "postore," and the absolute age of Post-Betze mineralization in the context of the overall spread in the dates presented in our paper. We address these issues in turn.

The postore sill, which we also loosely originally termed "dike," is important in that it brackets the timing of gold mineralization. Although Ilchik suggests that this intrusion predates mineralization, the weight of evidence is to the contrary. Whereas the postore sill is composition-ally similar to preore Goldstrike stock-equivalent rocks, it is texturally quite distinct. In fact, it was distinctive enough for us to map it out in the subsurface from drill core, something which we were unable to do for any of the other sills. Comparatively, the rock is little altered and it is the only one in the ore zone that retains primary bio-tite. Assays shown in figure 5 of Arehart et al. (1993) are the original assays done on 5-ft intervals before the core was logged; in some samples mineralized inclusions are present within the sample interval. More detailed analysis of this rock type, when clear of any inclusions of mineralized sedimentary rock, yields very low values for gold. This is true of samples from several core holes. In sharp contrast, the preore dikes and sills are all significantly altered and mineralized (i.e., well above background in areas of sedimentary rock mineralization), although they are generally of lower grade than the surrounding sedimentary rocks. We are well aware of the erratic nature of and lithologic control on gold mineralization in sediment-hosted disseminated gold deposits that are also seen at Post-Betze. Even taking this into consideration, it is clear that there is effectively no gold in the postore sill in comparison to significant gold in preore dikes and sills.

The Roberts Mountains of north-central Nevada are comprised of Paleozoic sedimentary rocks that host several gold deposits and subeconomic gold resources (Fig. 1). These gold occurrences are within a regional alignment of precious and base metal deposits in north-central Nevada termed the Battle Mountain-Eureka mineral belt (Roberts, 1966). Field relations and radiometric ages in three areas of the Roberts Mountains (Maher et al., 1990) allow assignment of minimum and probable maximum ages for gold mineralization. New radiometric age data from the Roberts Mountains and other precious and base metal deposits within the Battle Mountain-Eureka mineral belt are combined in this report with previously published geologic data to construct a metallo-genic framework for gold and other metallic deposits in north-central Nevada.

The Post-Betze deposit of Nevada is the largest sediment-hosted disseminated gold deposit presently known, both dimensionally and in terms of contained metal. Ore occurs primarily as submicron-sized gold that is disseminated in altered sedimentary rocks of the Lower Paleozoic Roberts Mountains Formation. However, significant portions of the ore are present in altered monzonite of the Goldstrike stock. Alteration and mineralization were controlled by both structure and stratigraphy. Alteration began with early decarbonatization and was followed by silicification and, finally, argillization. Phyllosilicate mineral zoning grades from proximal kaolinite to kaolinite + sericite to unaltered rock.

A granodiorite stock intrudes complexly folded and thrust-faulted Paleozoic sedimentary rocks in the Osgood Mountains of eastern Humboldt County, Nevada. Within the metamorphic aureole surrounding the pluton, the sedimentary rocks are converted to cordierite hornfels and marble; tungsten-bearing tactites developed along the contacts of the granodiorite. Cutting the granodiorite and sedimentary rocks is the Getchell fault, along which the disseminated gold ore bodies of the Getchell mine are localized. K-Ar ages of the granodiorite, andesite porphyry, tungsten-bearing tactites, and altered granodiorite from the Getchell mine indicate that emplacement, alteration, and mineralization are all part of a magmatic-thermal episode which took place approximately 90 m.y. ago.

Newly-recognised porphyry-style mineralisation within the Ertsberg intrusion displays significant differences from porphyry mineralisation at the Grasberg porphyry Cu-Au deposit. Stockwork mineralisation in the Ertsberg occurs near the giant East Ertsberg Skarn System, close to the northern margin of the intrusion. Stockwork mineralisation in the diorite is spatially associated with 5-15 m wide, E-striking, dykes of porphyritic hornblende monzonite that cut equigranular Ertsberg diorite. The porphyry dykes strike parallel to major district structures and occur where those structures project into the Ertsberg intrusion. Hornblende abundance greater than biotite, the much greater content of sphene, a paucity of broken phenocrysts, and the aplitic groundmass distinguish the porphyry dykes in the Ertsberg Stockwork Zone from the finer-grained groundmass Kali dykes of the Grasberg deposit.

The Wernecke and Southern Ogilvie Mountains in Yukon are part of an almost east-west trending range in the northern Canadian Cordillera in which several areas of the Palaeo-Mesoproterozoic basement are exposed, enveloped by a Phanerozoic miogeoclinal sequence. The oldest division, the -1.8-1.4 Ga Wernecke Supergroup, is interpreted as a "clastic rift'". It is an up to 15 km thick pile, the bulk of which is a monotonous, well-bedded siltite-quartz rich litharenite-argillite, topped by carbonate-pelite units. Less than 1% of the area consists of small gabbro to diorite intrusions of several, mostly Palaeoproterozoic and Mesoproterozoic, generations. The predominantly brittle deformation regime produced extensive tracts of disrupted and dismembered units grading to tectonic (not subduction !) melange. These have been overprinted by large scale Na, Ca, Mg, Fe, C02 and lesser Si, K metasomatism to produce widespread albitisation, chloritisation, carbonatisation, hematitisation and less extensive sericitisation (with local biotite) of the fractured sedimentary » magmatic rocks as well as tectonic fragmentites. The "Wernecke Breccia" is a metasomatised disaggregated breccia series and it is associated with hundreds of small scattered showings of specular hematite, magnetite and chalcopyrite, several occurrences of U and Co minerals, and anomalous gold. Not even a marginally economic orebody has so far been discovered despite intermittent exploration going back to the 1960s. It appears that we are dealing with a moderately deep (closely above the ductile-brittle interface) level of regional release and displacement of metals from source rocks (Fe, Cu and Co from gabbros; U perhaps from carbonaceous argillites) by metasomatic destruction of the carrier minerals. However, the system lacked sufficient plumbing and the channelling required to produce better metal accumulations at higher levels.

Within Peru, Fe oxide-Cu-Au deposits are found mainly in the Western Andes range and on the coast, associated with the Jurassic-Cretaceous alkaline to calc-alkaline volcanism of the aborted ensialic Canete-Huarmey Marginal Basin. They also exist in the calc-alkaline plutons of the Coastal Batholith and theTholeiite Patap Super-unit, associated with continental margin processes. The exception is Cobriza (100 million tonnes' @ 1.5% Cu, Fe oxide-Cu-Au type; Cu calcic distal skarn) existing in the eastern range associated with Permian Tardihercynian distensive tectonics and alkaline granites.