Hello, and welcome to the forum.
This is an interesting feature. Not knowing what kind of area your in makes it hard to guess what this is. Obviously the woodworks and ropes that were once attached to this feature are long gone.
The last photo you call a tang looks to me like a place where a rope or chain was anchored, probably to help support the feature.
In the very corner of some of the photos look like a shaft or well.
My guess, without knowing anything else, is that it is either a bellows setup for pushing air down into a pozo for a mine, or, it is a setup for drawing water from a well.
Also, it almost looks like some concrete at the base of this feature. Is that so?
Spaniards could certainly build structures such as this, but my guess is it's probably not spanish, without knowing any more than you posted.
I see some digging was done, possibly with the help of a metal detector? If so, what kind of metal was present?