Indeed, this study of stamps is a deep and spindly rabbit hole that is able to consume hours of my time between  admiring, photographing but mostly searching and reading.  Mr and Ms. Google are certainly most able and helpful partners but the fact that they can decipher a phrase as obscure as "Corrientes brown stamp."  remains amazing to  me.  However in this case they did.  I was referred of course to another friend Wikipedia who was glad to deliver a boatload of intelligence of the origins of this particular stamp.  For the sake of  brevity, this stamp is from the 1860-1880 period and from the "province" of Corrientes in Argentina.   The ability of the camera and zoom capability of the computer allow me to see detail that is far superior to even a very good magnifying glass....so respect again science and technology.  This is a giant leap from 8 years ago when I first actively pursued this hobby.  

  Corrientes is the capital city of the province of Corrientes which is about 160 miles from Buenes Aires.  They created their own stamps, which were also used for small change up until 1880 when the stamp business became centralized with the government of Argentina.  The design of the stamp came from (copycat actually) a french stamp  from that period that bore effigy to Ceres.  She apparently was the Goddess of growing plants according to Roman mythology.

  As to value, like most things  it depends on who wants it  and how badly.  This stamp is  not in good condition.  It is possibly a forgery  which oddly enough could make it more valuable.  From my very minor league research analysis,  value seems to be less than $100 on its best day.   

                                

   1895-1904 from Maritius, 4 cent value. Officially the Republic of Mauritius is an island  nation off the southeast coast of Africa, east of Madagascar.  At was to what was happening there at that time and  more detail as to the development and history of this stamp, I leave it to you.  Enjoy the chase.