Further sales of tax shelters in gold and silver mining claims in Colorado are prohibited by a consent decree entered into in Los Angeles federal court by the promoters, Gary Hoffman and American Marketing Associates. Under the tax-shelter proposal, Assistant U.S. Atty. Charles H. Magnuson said, investors were offered a tax write-off of six times the amount of cash paid to promoters through the device of signing notes that the promoter never intended to collect. The complaint also charged that the promoters falsely guaranteed that ore existed in commercial quantities on the mining property. Geologists said no body of ore exists there. It is estimated that the government would have lost in excess of $14 million in taxes if investors used all of the tax benefits.