I am requesting an appraisal for this artwork. It is an abstract composition of firm, angular black lines (appearing to be ink or marker) on a tan or cream-colored paper. The most relevant detail for the appraisal is that in the lower right corner, there is a handwritten signature in pencil that reads "Chillida," accompanied by a square monogram/stamp directly below it. The style and signature strongly resemble the work of the Spanish artist Eduardo Chillida. The piece is framed under glass, mounted on a white mat board (passe-partout), and set in a thick, ornate classic frame with gold and bronze finishes. I would like to request your expert opinion on its potential authenticity, the exact medium (whether it appears to be an original drawing or a print/lithograph), and an estimate of its current market value.

Regarding the dimensions, the drawing itself measures 18 x 18 cm, and the overall framed size is 55 x 45 cm.