The geological results of a borehole drilled to investigate the coincidence of centres of a zonal pattern of mineralization ( Dunham 1934 ) with areas of strong negative Bouguer anomaly are presented. The presence of a granite batholith with cupolas, postulated by Bott & Masson-Smith (1957) has been proved; the top surface of the granite was found at 1281ft depth and the boring was continued to 2650 ft in granite. The section begins in the Great Limestone at the base of the Namurian; a normal succession in the Middle Limestone Group (Lower Carboniferous) is revealed, the Smiddy Limestone with Girvanella Band being reached at 1056 ft 6in. The Lower Limestone Group differs from the section in Teesdale and the Pennine escarpment; in particular, beds equivalent to the Melmerby Scar Limestone, identified by their fauna of algae, corals, and brachiopods, have a rubbly lithology and are split by bands of seatearth, sandstone, and shale. Beneath them, clastic sediments 38 ft thick with marine fossils rest on the weathered surface of the granite. Two quartz-dolerite sheets were proved; the Little Whin sill, 6ft, is in the Three Yard Limestone as at Stanhope, while the Great Whin sill, 192ft 9in, lies beneath the Jew Limestone, stratigraphically lower than in Upper Weardale. The Weardale granite, carrying biotite and abundant muscovite, has a low-dipping foliation in the upper part, but this becomes less obvious below 2225ft depth. Preliminary X-ray studies indicate that low albite, orthoclase, maximum microcline, and forms intermediate between the last two are present. Analyses of representative rocks for major and trace elements are given. Xenoliths are conspicuously absent, but aplites and pegmatites are common. The mineralogical and chemical effects of weathering before Carboniferous sedimentation, and of the mineralization, are described. The borehole was sited near the crossing of the Boltsburn lead vein (ene-wsw) and the Red fluorite-iron vein (ese-wnw), both of which dip towards it. Strong metasomatic mineralization, including green fluorite, blende, and quartz occurs in the Tynebottom, Jew, and Lower Little limestones. Numerous small veins were also cut both in the sediments and the granite. Though chalcopyrite is present against the lower sediments, there is no evidence of a concentrated copper zone. Fluorite continues into the granite, and pyrrhotine, not present above, is found from 1355 ft depth. Mineralization continues to much greater depths than have previously been proved in the area; its source presumably lies beneath the granite cupolas, which may, however, have guided the rising fluids.
I. Introduction The North Pennine area of northern England, drained by the Tyne, Wear, and Tees and their tributaries, is a dissected plateau, uplifted along the Pennine fault-line to the west, and sloping gently down to the lowlands of East Durham. Its physiographic boundaries are, on the north, the main valley of the Tyne; on the west, the Pennine escarpment, overlooking the Vale of Eden; and on the south, the natural pass of Stainmoor. This region has been called the “Alston Block” by F. M. Trotter and S. E. Hollingworth (1928). Gently domed Carboniferous sediments resting on an eroded surface of closely folded Lower Palæozoic slates and volcanic rocks form the country-rock, and the area is structurally a fault-block, the limits of which correspond closely with the physiographic boundaries. The Carboniferous limestones, sandstones, shales, and coals have a total thickness of more than 5000 feet, and throughout their whole thickness rhythmic alternations of beds are well exhibited. In the Carboniferous Limestone series (S 1 -D 1 ), which is the lowest Carboniferous member, limestones predominate. Limestones are co-important with sandstones and shales in the overlying Yoredale series (D 1 -D 3 ), but are absent from the higher horizons. Coal seams alternating with sandstones and shales make up the Upper Carboniferous succession. As a result of the gentle outward inclination of the beds from the highest part of the dome, near Cross Fell, progressively higher horizons outcrop round the northern, eastern, and southern margins of the area. The Millstone Grit thus appears along the Tyne valley and over
Summary The primary object of the work was the investigation of the geological environment of the galena-fluorite-barite deposits. The Carboniferous Limestone Series, over 1400 feet in maximum thickness, was mapped in six divisions covering faunal horizons from ?C 2 S 1 up to and possibly above D 2 . The Millstone Grit Series rests unconformably on horizons from the Davidsonina [ Cyrtina ] septosa band in D 1 up to beds with Orionastraea , the relations being ascribed to a pre-Millstone Grit uplift, possibly domal in form, accompanied by faulting. Within the Millstone Grit the "Top Limestone" (renamed the Cockhill Limestone) was proved to be characterized by Cravenoceras cowlingense (E 2 ). Two higher marine horizons, well known elsewhere, were established here by many exposures : the Colsterdale Marine Beds, characterized by Cravenoceras nitidum (E 2 ), seen in the same section as the Cockhill Limestone, and the glauconitic Cayton Gill Beds. A structure-contour map based on horizons in the Millstone Grit mapped at surface and underground shows that the anticline in the southern part of the area, trending east-north-east, has an amplitude of about 1000 feet, and that a series of domes and basins have been developed along its crest. The North Craven Fault, runniilg along the southern flank of the anticline, is a complex fracture-belt enclosing a tight syncline in the western part of the area, degenerating eastwards into a small strike-fault. The eastern half of the Bycliffe Vein-system is mineralized up to the Cayton Gill Beds but the remaining veins are mineralized only in the Carboniferous Limestone. The most important ore-shoots are found in the upper division of D l , in limestone underlying either shales low in the local D 2 or the basal shale of the Millstone Grit, depending on the position of the unconformity. Less important ore-shoots are found at various horizons from ?C 2 S 1 up to D 1 . It is suggested that extension of mineralization in depth beyond the limits so far revealed is possible in the case of ore-shoots related to shale overlying D 1 limestone. There is a crude zonal arrangement of minerals. Palaeontological notes are included on Hederella cf. chesterensis (of a suborder new to Britain) and on two new forms, Productus (Eomarginifera) tissingtonensis cambriensis and Eumorphoceras bisulcatum grassingtonensis .
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