The Proceedings of the Eighth International Conference on Creationism (2018)

evidence that hot acidic waters rose to the earth’s surface and even produced ore deposits (for example, Franklin et al. 2005; Simmons et al. 2005), in the process they produced hydrothermal alteration that has distinctly different minerals and patterns of minerals than found in supergene ore deposits. Second, could oxygenated surface waters have been forced hydrodynamically downward in the receding waters phase of the Flood and accomplish the same supergene alteration? It is possible that some surface water would penetrate downwards, but as noted above, the chemical weathering that produces supergene minerals only occurs in the oxidizing zone above the water table where it is drier, and air reaches down from the surface (Dill 2015; Reich and Vasconcelos 2015). Besides, as noted above, the chemical reactions that produce the supergene minerals (see the Appendix) take decades to generate ore deposits from the repeated wetting and drying of the chemical weathering profile. 5. The Radioisotope Ages of the Supergene Minerals In conventional terms, the earliest dates of formation of these supergene minerals is at 70 Ma (Fig. 1). That is just before the K-Pg boundary, currently determined at 66 Ma (Gradstein et al. 2012). And then the frequency in numbers of mineral dates of formation per absolute date increases steadily up through the conventional Cenozoic. This frequency pattern is the same for global Mn oxide 40 Ar/ 39 Ar ages (Fig. 1a), global goethite + hematite (U-Th)/He ages (Fig. 1b), and Andean alunite-jarosite 40 Ar/ 39 Ar ages (Fig. 1c). However, it is interesting that the dates of formation of alunite and jarosite in the Andes really only start around 40 Ma, and then peak in frequency around 15-20 Ma (Sillitoe and McKee 1996). This is, in part, because many of the primary (hypogene) porphyry copper deposits only formed during the mid-Cenozoic, at the time when the Andes were being built by the active plutonism and volcanism associated with the subduction of the Pacific plate under the South American plate. So, the supergene minerals then only formed subsequently from those deposits after they formed in the mid-Cenozoic. That the chemical weathering responsible for the supergene minerals was connected to the present climate and landscape development was demonstrated conclusively by the U-series dating of supergene assemblages in Chilean porphyry copper deposits by Reich et al. (2009) It is similarly relevant and significant that the most recent set of goethite (U-Th)/He ages from the Hamersley region of northwestern Australia closely parallel the global goethite + hematite (U-Th)/ He ages in Fig. 1b (Miller et al. 2017). The Hamersley province is a passive continental margin with a moderately elevated (~800 m) interior composed of ridges and plateaus dominated by chemically resistant Archean to Paleoproterozoic banded iron formations (BIFs) and quartzites, and incised valleys consisting predominantly of shales and dolomites (Vasconcelos et al. 2013). The region has been structurally stable with little erosion for the entire Cenozoic. Much of the elevated interior is blanketed with ferruginous weathering profiles and related deposits, many of which are exposed and accessible in iron ore mines or prospects. The prolonged process of iron mobilization and precipitation, along with later cycles of dissolution and reprecipitation of existing iron oxides, has produced a thick horizon rich in goethite with readily visible and physically separable growth zones that supposedly span many millions of years (Heim et al. 2006; Vasconcelos et al. 2013). For such samples forming at earth-surface conditions, their goethite (U-Th)/He ages are established upon mineral crystallization (Shuster et al., 2005). Goethite acquires oxygen from the water in which it forms, and after that there is no open-system behavior of the oxygen or helium in the goethite (Yapp 1991). Thus, these (U- Th)/He ages date the formation of the goethite at the water table near the surface of this Precambrian terrain (Miller et al. 2017). Most creation geologists would regard this Precambrian terrain as pre-Flood, and likely even formed during the Creation Week (Snelling 2009). For this terrain to now be exposed in the post- Flood world implies that whatever strata were deposited over it and covered it during the Flood were eroded away by the retreating Flood waters, which also eroded much of its present topography. Thus, the goethite in the present weathering profile had to form after the Flood waters retreated and the ground surface dried out, with weathering and goethite formation commencing as the Flood ended and the water table was subsequently lowered. The goethite (U-Th)/He ages span the Cenozoic from 70.5 Ma to 4.8 Ma, with intermediate ages of 68.0 Ma, 61.7 Ma, 47.3 Ma, 26.0 Ma and 8.5 Ma (Miller et al. 2017). These ages plot within the spread of ages in the histogram in Fig. 1b and are also consistent with the same pattern of 40 Ar/ 39 Ar ages for Mn oxides and alunite-jarosite in Fig. 1a and 1c respectively. Other examples further substantiate this pattern for the timing of supergene mineral formation. The supergene iron and manganese ore deposits of Minas Gerais, Brazil have developed at the present land surface from early Precambrian banded iron formations and Mn-rich sedimentary units, so the 40 Ar/ 39 Ar ages for the supergene minerals are all Cenozoic (de Oliveira Carmo and Vasconcelos 2006; Spier et al. 2006). Similarly, in Africa supergene manganese deposits have developed at the present land surface on Proterozoic (Precambrian) sedimentary units in the Katanga (De Putter et al. 2015), Kalahari (Gutzmer et al. 2012) and Burkina Faso regions (Colin et al. 2005; Beauvais et al. 2008), and the 40 Ar/ 39 Ar ages for Mn oxides are all Cenozoic, some of them being plotted in Fig. 1a. In China Mn oxides have developed at the surface on Devonian carbonates (Li et al. 2007), while in India Mn oxides have developed in laterites due to chemical weathering of the underlying Cretaceous Deccan basalts (Beauvais et al. 2016; Bonnet et al. 2014, 2016). In both instances the 40 Ar/ 39 Ar ages for Mn oxides are all younger Cenozoic, indicative of the chemical weathering at the current landscape surface. In Australia the Permian Mt. Leyshon epithermal gold deposit and its surrounding hydrothermal alteration reach close to the present land surface from where chemical weathering has penetrated down to produce supergene alunite-jarosite group minerals in the host rocks and ore (Scott 1990). K-Ar ages of these supergene minerals are late Cenozoic, similar to 40 Ar/ 39 Ar ages for Mn oxides in the current weathering profile in a nearby part of Australia (Feng and Vasconcelos 2007). Similarly, in Spain the late Paleozoic Las Cruces volcanogenic massive sulfide deposit was exhumed and affected by subaerial oxidation connected to the current landscape (Tornos et al. 2017). 40 Ar/ 39 Ar dating of supergene alunite yielded Snelling ◀ Flood/post-Flood boundary ▶ 2018 ICC 559