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The manganese minerals are psilomelane, hausmannite, braunite, 

 manganite, pyrolusite; and wad. Psilomelane is most abundant. 

 Iron oxides (limonite and hematite), and ferruginous manganese ores 

 (hematite and limonite with psilomelane), barite, quartz, calcite, 

 arsenopyrite, and sulphides of the heavy metals are also associated 

 with the ores. The workable manganese and ferruginous manganese 

 deposits occur under the following conditions: (i) replacement de- 

 posits in the Cason shale and its residual clay; (2) replacement 

 deposits in the Fernvale limestone; (3) residual deposits from the 

 Fernvale limestone; (4) replacement deposits in clays; (5) transported 

 stream-gravel deposits. Of these, (3) is most important as a source of 

 manganese ores, and (i) has furnished more ferruginous manganese. The 

 replacement deposits in the Cason shale and its residuum occur in 

 irregular masses, "buttons," or horizontal seams and beds; "buttons" 

 of red iron oxide are also found under similar conditions. The occurrence 

 of manganese-bearing calcite suggests that all the manganese oxides 

 were derived from the carbonate. A similar origin for the manganese 

 replacements in the Fernvale limestone is well demonstrated by deep 

 cuttings in the district: here cores of carbonate are found surrounded 

 by envelopes of oxides of manganese and ferruginous manganese. 



The largest yield of manganese ore, the largest reserves, and a 

 considerable part of the low-grade ore output comes from the residual 

 deposits of the Fernvale or lower limestones, into the deeper portions of 

 which the nodules were settled by gravity or were washed by streams. 

 The decomposition of the limestone has formed manganese-bearing 

 surface hollows and channels; elsewhere manganese-bearing caves and 

 sinks have developed. Slumping and sinking of the soft, plastic clay 

 (and of the overlying Cason shale) have greatly disturbed the ore bodies. 

 These residual deposits consist of psilomelane, hausmannite, wad, and, 

 subordinately, braunite. The hard oxides may occur as bowlders that 

 weigh as much as 22 tons; generally the coarser the masses, the more free 

 the ore from iron and the higher its grade. 



Some small deposits of manganese oxides have been formed by the 

 introduction of manganese into the clays through the action of ground 

 waters ; such manganese probably came from the Cason shale or Fernvale 

 limestone. These ores are low grade and diluted though the presence 

 of silica, iron, and alumina. 



Finally some manganese is obtained from alluvial cones and gravel 

 bars, the deposits being composed of compact masses of manganese oxides, 

 and of small pebbles of oxide of iron. Many of the largest concentrations 



