I dont want to generalise,but Ive seen photos of some Chinese slate quarries,where conditions are poor.people carrying slabs on bamboo poles,hard hats are made out of wicker etc.,and can only assume this plays a part.assuming insurance and other overheads are (relatively) low compared to europe,this also may contribute.Some years ago I was talking to a roofing merchant who wouldnt stock Chinese slate because of the working conditions in the quarry.Also it is by far inferior to Spanish slate,let alone welsh slate.Probably good for flooring and slab though (if it doesnt change colour).im sure quarry conditions there will eventually change,but while they are comparitively poor,people will still be happy to buy inexpensive slate in the `international economy`.
Tis a shame these people spend a fortune on their `Grand Designs`and then cut costs on the roof.Incidentally,Brazilian slate can sometimes be nearly impossible to cut by hand. `A false economy`and `you get what you pay for`spring to mind.