Outcrop samples weathering

The Battle Creek, Wyoming outcrop sample has substantial amounts of vanadyl porphyrins, indicating that petroporphyrins may be preserved even after prolonged exposure to weathering agents. 

Gawler Craton, located on the edge of the Great Victoria Desert (GVD). In this part of the GVD, regolith landforms are comprised of scarce hills of weathered bedrock outcrops surrounded by sand spreads, dunes and colluvial materials the hills act as windows to the otherwise covered weathered bedrock. The outcrops themselves have been silicified and, more recently, have been overprinted with calcrete. Calcrete sampling is relatively easy on the exposed outcrops and is preferentially sampled by mineral explorers due to its near-surface location (<10-20 cm depth). However, calcrete on the colluvial slopes and in the swales is not as easily located because of concealment by GVD sand and colluvium. 

The organic materials extracted from a number of domestic tar sands contain various amounts of vanadium and nickel, sometimes in substantial quantities. Metalloporphyrin complexes of these two metals have been detected in some outcrop and shallow core samples. If these porphyrins are indigenous petroporphyrins, it is evident that these compounds can survive weathering processes. 

Discrepancies between reactive and adsorption surface area may also be related to the presence of deep etch pits or pore outcrops which can constitute transport-limited micro-environments for dissolution (Jeschke and Dreybrodt, 2002). Much of the BET surface area for some alkali feldspars used for dissolution in the laboratory has been attributed to grinding-induced microporosity (Hodson et al, 1999), and such pore outcrops are candidates for transport limitation. If such induced surfaces react dilferently than surfaces of weathered samples, then the BET surface area may be an inappropriate parameter to use for extrapolating interface-limited kinetics from laboratory to field (Lee et al, 1998 Brantley and Mellott, 2000 Jeschke and Dreybrodt, 2002) and consideration may need to be given to length and extent of grinding for laboratory samples (Hodson, 1999). It may be more appropriate to use geometric rather than BET surface area to extrapolate kinetics for samples where etch pits or pore outcrops are important contributors to BET surface area (Gautier et al, 2001 Jeschke and Dreybrodt, 2002 Mellott et al, 2002). 

Channel sampling is one of the best methods for sampling in-seam coal. When the coal sample is collected from an outcrop, the exposed area should be cleaned to avoid the weathered exposed coal surface. Normally, a small box cut is made at the coal outcrop exposing the entire thickness of the coal seam. For a relatively thin seam, only one coal section is recommended. However, if the seam is thick, two or more coal sections may be necessary to sample entire seam. 

The outcropping of the fault zone under study was dug during the construction of the 212 National Road, presenting a fresh and clear fault zone with a width of 50 m. Four fault gouge samples with different colors, two host rock samples, a weathered host rock sample were collected (Table 1, Figure 2). 

A first example concerns a sample from a weathered boulder in a granite outcrop in Sungai Ringit (Malaysia), which is relatively rich in hematite. The spectra at RT and at 80 K are displayed in Fig. 3.38. 

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