Mining Memorabilia - Historical mine drawing, Almaden Mercury Mine, Spain

We have an undated, but authentic, drawing of the underground mine workings of the Almaden Mine in Spain. The Almaden Mine is a recognized World Heritage Site by UNESCO and the area was active from the 1600s to 2000! This historical piece was purchased from Arader Galleries in San Francisco back in 2008 and was recently part of Allen Ingelson's collection. We are estimating this drawing was made around 100 or more years ago. Matted dimensions: 39.5 cm x 43 cm