2 The Patio and Cazo Process. 



The Cazo method was invented in 1609, in Peru,* and lias 

 not been used much except in South America and Mexico. 

 The Patio method is used in Mexico on ores that have a mean 

 yield of from thirty to sixty dollars to the ton. Ores of much 

 higher grade than this are treated, provided they are not refrac- 

 tory, but when they are rebellious they are generally treated by 

 fusion. In order to do this, however, the yield must be large, 

 for fuel is very dear on the plains of Mexico. 



It is quite rare that anything is done to the ores befoiv 

 treatment, except hand-picking to sort out those of high grade 

 from those of less yield, and to remove some of the sterile 

 material. Occasionally, however, they are treated in a rude 

 Avay. At Zaeatecasf very impure ores are broken by hand into 

 small pieces, made into a pile surrounded by a rude wall laid up 

 dry, and imperfectly roasted with charcoal. In the districts of 

 Tasco and Sultepec, where sulphurous ores are abundant, they 

 are roasted with wood in the same furnace, comalillos, in which 

 the magistral is made, but not efficiently, though the operation 

 lasts twelve hours. The colas, the concentrated sulphides, are 

 also roasted in piles. This pile-roasting is not only very insuf- 

 ficiently done, but is very uncertain in its results. The object 

 is to remove the substances which attack the mercury, but 

 owing to defects both of fuel and arrangement of the pile, but 

 little results from it, beyond the blind following of a routine 

 which lias little other reason than that it has been practised 

 somewhere else. There is always danger that, in roasting these 

 ores, the heat will be raised sufficiently high to melt them. 

 When they are rich, a fusion treatment is much more rational. 

 It is doubtful whether, with a dear fuel, much is gained by 

 roasting previous to the treatment on the patio. 



It is generally the gangue which determines the name of the 

 ore, but it is sometimes called after its size. Quartz is called 

 guija, and quartzose ore guijoso ; feldspar is called caliche ; feld- 

 spathic ores, calichoso. When there is much gangue it is said 

 to be desploUaclo. Quemazon is a black porous decomposed ore. 

 Large pieces of the first and second class ores are called gabarro. 

 The smalls are called metal granza. » 



* Percy's Silver and Gold, Part I, p. 656. 



+ Phillips's Gold and Silver, p. 352, London, 1867. 



