Mining Early production was from near – surface shafts and crosscuts.  Stoping (ore removal) quickly commenced, using native timber for support, but difficulty was soon encounted with the heavy, friable oxidised ore.  The quare set system of timbering using imported oregon was introduced by William Patton at the BHP Mine in 1888, but with the increasing size of stopes (space left after removal of ore), extensive creeps occurred as the unfilled sets collapsed.  The heavily timbered stopes were also a significant fire hazard and several disastrous fires occurred.  Initially, mill residues could not be used for backfilling because of their high metal content and were stockpiled at the surface awaiting treatment. BHP commenced open cutting of the hill in 1891 to relieve the weight on the stopes below.  By 1906, a hole 1.2 kilometres long and 90 metres deep had been excavated. Subsequently, other mines at the crest of the lode operated open cuts.  As the mines deepened, the oxidised ore was depleted and attention turned to the mining of the underlying sulphide ore.  The sulphide orebody was harder and more compact, allowing modern mining methods to be introduced in the early 1900s.  Horizontal cut and fill stoping was adopted to remove ore using mullock and, later, mill residues as filling.  This method is still general practice today although the scale and degree of mechanisation have changed dramatically. Longhole stoping was introduced at the NBHC Mine in the 1970s.  In this method, parallel holes are drilled up to 24 metres into the ore face, which is then blasted with explosives.  Broken ore is removed by machine, leaving huge stopes up to 50 metres high, 70 metres long and 10 metres wide separated by pillars.  The stope is filled with mill residue which is pumped hydraulically from the surface.  Pillars of ore are left in heavy ground or later extracted by square set stoping. Between 1976 and 1991, MMM reworked the central part of the line of lode by open – cut methods, stripping away vast amounts of overburden to gain access to remnant low – grade ore and old tailings.  Open – cut operations were carried out at the North Mine between 1985 and closure in 1993.