Opal locality, Brazil

Wondering if anyone knows the locality for this matrix opal? Was available by the barrel in the early 80's. Appears to be opal filling vugs in a brecciated volcanic rock. The vugs are lined with small pyrite crystals, then filled with jelly to crystal opal.
Thanks, Bob
Specimen is 3 inches across

have a look here:
[www.mindat.org]

Looked at this locality on Mindat, but didn't seem to occur in vugs, more like coatings on fracture surfaces, akin to Painted Ladies from Lightening Ridge.

I have similar material in my collection, also acquired on the 1980's; the locality is by sure Pedro II, Piauí state, but it is not necessarily from Boi Morto mine, there are several other small mines on the area.

Thanks, Luis, following your info I found this very detailed report: boletinsgm.igeolcu.unam.mx/epoca04/6201/(7)Barreto.pdf

Bob

Bob, I could not connect to the link via Google; on which magazine was it published?

Hi Luiz,

Try this link: [boletinsgm.igeolcu.unam.mx]

Ron