Hi Olav,
The "21st Street" specimens were collected in July 1998 by Gary Hoffman of Colorado Springs. The specimens from the area are no longer accessible because a roadway covers the area. A road construction cut revealed the specimens. A local (Colorado Springs) mineral dealer helped collect and bring these to market. The specimens I once had consisted primarily of Calcite with some golden Barites. The geology of the area is definitely not igneous as you postulated. I can only speculate, having owned a few pieces, that the mineralization in the area is strictly post evaporative in regards to its genesis.