Outcrop samples location

Another type of variation, observed for outcrop samples in Labrador as well as in the eastern United States (9,JO), is shown in Figure 4. In this case, each separate outcrop located within several miles of the other... 

Fig. 1. The Belingwe greenstone belt, Zimbabwe, showing sample locations. The thin Manjeri Fm (including Spring Valley, Shavi, Rubweruchena and Jimmy Members, not shown here) outcrops along the base of the main (Upper Greenstones) syncline.

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. 

Often samples from outcrops are collected with little knowledge of the geologic settings. While a geographical description of a location is important, it can be misleading. For example a series of soapstone samples taken from Lancaster and Chester Counties in southeastern Pennsylvania... 

Figure 4. Cross-section of Neptune s Grotto flowstone ( 73 cm thick), unconformably overlying Triassic marble. Black arrows indicate outcrop-scale disconformities (numbered I to IV). Numbered sections on the left correspond to text descriptions. The white arrow shows a broken stalactite resting on a disconformity surface. The open triangles to the right of the graph indicate stratigraphic locations of U-series samples.

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