We have seen a few logo marks like this before, but had no luck at all in tracking them down. The logo mark is the classic "three-peaked Fuji" with what appears to be a fence or possibly a stylized version of the character 井("well," as in a wishing well).
I know of no resource in English that catalogues Japanese makers' marks of small metalwork like this. There has been some discussion in this section of damascene, and FredZ has a site that shows some makers' marks: https://plus.google.com/photos/10243567
It looks to me like this piece started out as a buckle and was later refashioned into a brooch, so I would assume it dates from some time before WWII and was altered or repaired in the immediate postwar.
You might also try posting a query to a jewelry discussion forum. Please keep us informed if you find out something more.