Hello ......Yes I have personally opened a COMPLETELY sealed, back filled cave . Portions (including entry) were sealed up with caliche, two areas were sealed with stacked, cemented (13 plus feet of wall) , then covered with a glaze to look natural. It was only after finding the symbols inside that corresponded to the exterior rock map that we narrowed the site to Spanish, (or Mexican) from the 1500-1600. (from the writing)
After excavating thru the fill. we found a Hand Arrastra formed in the floor. The entire thing had been chiseled out of solid bedrock. The floor was like a big cereal bowl with a putting green cup hole in the center of the bowl. We found a schematic of the room in Chuck Kenworthy's Death traps book. His book states the hand arrastra was used only in the mining of rich pockets of visible gold. (One of the mysteries since geologist say there is no hard rock gold in the Ozarks Karst geology)
We are regrouping to proceed down the Pozo that had also been concealed . We are trying to access a vault without dealing with the death trap.
In answer to your question...YES others have found evidence of Spanish and others walling up and disguising chambers in caves, and cave entrances as well.
The Old Spanish Treasure Cave in Gravette, Ar. has uncovered many sealed areas of their cave...Old artifacts are on display in the shop.
Have you tried to take the up close ....flash on.... pics we discussed?
Clueman