alkanes or other hydrocarbons as well as inert gases such as nitrogen helium or argon the hydrocarbon substrate preferably comprises at least about 50 weight percent butane more preferably the hydrocarbon substrate comprises at least about 90 weight percent butane in a particular embodiment the hydrocarbon substrate comprises at least about 99 weight percent n butane the butane may contain straight n butane and or branched chained compounds such as iso butane suitable hydrocarbon utilizing bacteria may include the following groups in addition to fungi algae protozoa rotifers and other aerobic and anaerobic microbial populations found in decaying materials in addition suitable bacteria may include facultative anaerobes and microaerophilic anaerobes which are capable of surviving at low levels of oxygen these bacteria do not require strict anaerobic conditions such as the obligate anaerobes acidophilic alkaliphilic anaerobe anoxygenic autotrophic chemolithotrophic chemoorganotroph chemotroph halophilic methanogenic neutrophilic phototroph saprophytic thermoacidophilic and thermophilic bacteria may be used hydrocarbon and oxygen injection may encourage the growth of other microorganisms such as fungi protozoa and algae that may be beneficial to the metal recovery process the injected oxygen may be in the form of air e g dry air comprising 20 9 percent oxygen a gas stream with varying.