Marathon Patent Group (MARA) withdrew its offer to purchase Fastblock Mining after the two companies failed to reach a long-term agreement on power rates.MARA rises 0.5% in after-hours trading.During due diligence, Marathon found that the power agreement, under which Fastblock would provide power at a subsidized rate of $0.0285KwH, would expire in three years.The two companies were unsuccessful in extending the term of that agreement to a seven- to 10-year window.Without that extension, the acquisition would not be economically feasible, Marathon said.Marathon has, instead, executed a term sheet with an alternate power company to provide 104MwH of power at $0.028KwH for 11 years.Previously: Marathon Patent buys Fastblock Mining in an all-stock transaction (Aug. 26)