Pipes, breccia

Collapse Breccia Pipe Deposits. The primary occurrence of coUapse breccia pipe deposits is in circular, vertical pipes fiUed with down-dropped fragments. Uranium is concentrated in the permeable breccia matrix and in the accurate fracture zones enclosing the pipe. An example of... 

Collapse breccia pipe Deposits in the Arizona strip in Arizona, USA. 

Local dissolution features are recognized in the Delaware Basin. These may be of either shallow or deep origin, and it is the latter which may pose the greater potential hazard to the repository. These features, often called collapse chimneys or breccia pipes, form when localized dissolution occurs deep in the evaporite section, possibly at the base of the salt beds, resulting in a cavern into which overlying beds... 

Wenrich, K.J. and Silberman, M.L. (1984) Potential precious and strategic metals as by-products of uranium mineralized breccia pipes in northern Arizona. AAPG Bulletin, 68(7), 954. 

Edwards A. C., Lovering J. F., and Ferguson J. (1979) High pressure basic inclusions from the Kaymnnera kimberlitic breccia pipe in New South Wales, Australia. Contrib. Mineral. Petrol. 69, 185-192. 

Chen Y. D., O Reilly S., Griffin W. L., and KroghT. E. (1998) Combined U-Pb dating and Sm—Nd smdies on lower cmstal and mantle xenoliths from the Delegate breccia pipes, southeastern Austraha. Contrib. Mineral. Petrol. 130, 154-161. 

Mineralised breccia pipes occur in Palaeozoic sedimentary rocks of the Colorado Plateau in northern Arizona (Weinrich, 1985). These pipes are usually circular or oval at suboutcrop, have horizontal dimensions that are typically a few tens of metres and vertical dimensions that may extend to 1000 m. They appear to have developed over solution-collapse structures resulting from karstic weathering of Lower Mississippian carbonate sediments between the Upper Mississippian and Triassic. The mineralisation, comprising pitchblende and sulphides of Fe, Cu, Mo, Pb and Zn, is found beneath a massive pyrite cap, several hundreds of metres below surface. Some of the ore bodies are, or have been, mined for uranium. Gangue minerals include calcite and dolomite. 

Fig. 14-11. Carbon dioxide in soil air (sample sites and contours in %) over mineralised breccia pipe, northern Arizona (from Lovell and Reid, 1989).

Figure 14-11 shows contoured soil-air CO2 data collected from a depth of 1 m, overlying a breccia pipe which is heavily mineralised at depths of 150-250 m. The anomaly peak is only 0.3% CO2 (only ten times the atmospheric background) but the circular gas halo is centred over the mineralisation (Lovell and Reid, 1989 Reid and Rasmussen, 1990). The fact that these low concentrations accurately reflect mineralisation at these depths is a testament to the sensitivity and precision of the gas-chromatographic method of analysis that was used, and to the low background. 

Reid, A.R. and Rasmussen, J.D., 1990. The use of soil-gas C02in the exploration for sulphide-bearing breccia pipes in northern Arizona. J. Geochem. Explor., 38 87-101. 

Weinrich, K.J., 1985. Mineralisation breccia pipes in northern Arizona. Econ. Geol., 80 1722-1735. 

White and McClintock (2001) divided the breccia pipe (or diatreme) in Fig. 12.5 into three sections which they identified as ... 

The phreatomagmatic volcanic eruptions expelled both compressed gases and rock fragments and formed shallow maar craters at the surface surrounded by a tephra ring. The superheated steam that was discharged caused pervasive hydrothermal alteration of the breccia pipes and associated pyroclastics, including the deposition of zeolites in the open spaces of the... 

Fig. 12.5 The phreatomagmatic volcanic diatremes were subdivided by White and McQintock (2001) into a root zone (RZ), a lower diatreme section (LD), and an upper diatreme section (UD). The explosions that break up the country rock occur in the root zone where large volumes of water interact with basalt magma rising from depth. The cone shaped breccia pipe is composed of angular fragments of country rock and basalt in a matrix of powdered rocks and is capped by a maar crater that vents steam and other gases. The crater is surrounded by a ring of tephra and rock fragments ejected by the explosions (Reproduced by permission of J.D.L White and the Geological Society of America)...

Monogenetic and polygenetic breccia pipes related to easttrending faults cut the volcanic sequences they are probably the vents of volcanic units that exist in a higher stratigraphic position in the Collio formation. 

Inliers or windows where salt is locally thin or absent from an area that is surrounded by salt usually indicate dissolution of salt, provided that the feature cannot be explained reasonably as a depositional feature. Examples of such inliers were shown by Jordan and Vosburg (1963) in the Flowerpot salt in Beaver County, Oklahoma, and evidence of such dissolution is found in the breccia chimneys and pipes [see (6) above]. 

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