Peguy, many fine guns have been made in the Basque city of Eibar. I am unfamiliar with the "Marixa" name, and it does not appear in Terry Wieland's book Spanish Best (which has a list of manufacturers in business in the region in 1972). The value of the gun is therefore based on its quality and condition, not on the value of a brand name. A more complete description of the gun is needed.
Spanish guns are date stamped with a code. The code is in the form of a letter and a number. For example, A1 is 1955, B1 is 1956 etc. The code can be found on the action flats of the gun or on the underside of the barrels (you will have to take the barrels off the gun). There will be a number of other proof marks under there, and some numbers as well. These all signify something, and can be read to provide such info as chamber length and service load, and the weight of the barrels. Pictures of the gun and the proof marks would help greatly in determining value - the Spanish made everything from junk to some of the best shotguns you can imagine. It is normal for the barrels to have different chokes, the gun allows you to choose the appropriate barrel for the shot.
Sharptail
