On the Pampas, Or the Young Settlers by G. A. Henty

Historical novel set in Argentina in the 19th century. According to Wikipedia: George Alfred Henty (8 December 1832 - 16 November 1902), referred to as G. A. Henty, was a prolific English novelist, special correspondent, and Imperialist born in Trumpington, Cambridgeshire, England. He is best known for his historical adventure stories that were popular in the late 19th century. His works include Out on the Pampas (1871), The Young Buglers (1880), With Clive in India (1884) and Wulf the Saxon (1895).