Stock certificates issued by mining companies during the 20th century have been increasing in value in recent years. Bloggingstocks.com offers a number of example certificates, including Phelps Dodge, Magma Copper Company, Arkansas and Arizona Copper Company, and United Western Minerals Company. Prices at the beginning of this decade were typically $4 or $5 each with some as high as $10, but are now running $40 - $60, resulting in investment returns (on the paper certificates, not the mines!) of 500% to 1100%.
[right, a certificate for 1000 shares of the Arkansas and Arizona Copper Company. Bloggingstocks.com says "the firm mined properties in the northernmost sector of the Verde Mining District of Yavapai County, Arizona. The certificate was issued in November of 1916 and indicates total authorized capital stock of $6.75 million. The piece was printed by the American Bank Note Company, a historically important engraver of currencies, postage stamps and stock/bond certificates. This specimen is up 500% ($10 to $60) in seven years."]