This work was first published in Zimbabwe (or one of its antecedents) and is now in the public domain in Zimbabwe because its copyright protection has expired by virtue of the Copyright and Neighboring Rights Act, enacted 2000 (details). The work meets one of the following criteria:
It is an anonymous work or pseudonymous work and 50 years have passed since the date of its publication (or creation, whatever date is the latest)
It is a collective, audiovisual or photographic work, and 50 years have passed since the date of its publication (or creation, whatever date is the latest)
It is a sound recording or broadcast and 50 years have passed since the date of its publication
It is an artistic, literary, or musical work created under the direction of the state or an international organization and 50 years have passed since the date of its publication
It is another kind of work, and 70 years have passed since the year of death of the author (or last-surviving author)
It is one of "official texts of enactments, bills prepared for presentation in parliament, official records of judicial proceedings and decisions, other material published in the Gazette, official texts of international conventions, treaties and agreements to which Zimbabwe is a party"
A Zimbabwean work that is in the public domain in Zimbabwe according to this rule is in the public domain in the U.S. only if it was in the public domain in Zimbabwe in 1996, e.g. if it was published before 1946 and no copyright was registered in the U.S. (This is the effect of the Uruguay Round Agreements Act (17 USC 104A) with its critical date of January 1, 1996.)
Uploaded a work by Horizon magazine published this in 1964 from http://www.nrzam.org.uk/Site%20Resources/Abercorn_Documents/Gamwell%20Sisters%20v02-10-17.pdf with UploadWizard