Britain's longest maze cave: Hudgill Burn Mine Caverns, Cumbria, UK

摘要

In 1816 miners in the Hudgill Burn Lead Mine near Alston in Cumbria broke through from a mine level into "a [natural] cavity which was large enough to travel in ". However they and later Georgian and Victorian "tourist" visitors only explored a few hundred metres of what was clearly an extensive maze cave before the mine closed and the subsequent collapse of mine passages rendered the cave inaccessible. In the late 1990s the Cumbria Amenity Trust Mining History Society reopened the mine and regained access to the cave. Over 2013-2014 the Moldywarps Speleological Group has carried out a thorough exploration and survey of the system. The cave is in the Great Limestone at the top of the Visean and is sandwiched between beds of sandstone and shale. The phreatic network system has a reticulate geometry and is enclosed in an area of about 34,000m~2 with most passages aligned on and parallel to four major joint sets. In contrast to many maze caves, the system is two-dimensional comprising only one storey, and lies on an essentially planar surface. The cave has a surveyed plan length of 13.24km, making it the longest maze cave in Britain. The system shows some of the characteristics of transverse hypogenic speleogenesis, having no apparent relationship to the present landscape, a high passage density and high areal coverage. However, it is the presence of several dissolution features known as the morphological suite of rising flow that provides support for the hypothesis that the maze cave system has developed by hypogenic rather than epigenic means. The proximity of mineral veins containing galena and cerussite, the former oxidised by secondary mineralization processes to yield the latter and sulphuric acid, has probably influenced passage inception and development. A distinctive feature of the cave is the presence on all walls and ceilings of "sooty" black or dark brown deposits, identified by XRD and Raman microspectroscopy to be a highly zinc-sorbed birnessite-type phyllomanganate with a structure and zinc content that approaches chalcophanite. The source of the zinc is probably sphalerite, originally present as a primary mineral, that has undergone subsequent oxidation to smithsonite, convertible to soluble cations capable of sorption into birnessite-type minerals. The presence of these phyllomanganate deposits indicates the probable action of cave microorganisms in assisting the oxidation of Mn(II) oxides to tri- and tetra-valent species and the further dissolution of cave features through acidic metabolic by-products.